Chapter 4 - Mutation and Variation

Question 1

Mutation

Answer 1

= a process that produces a gene or chromosome that differs from
the wild type

Question 2

Mutation =

Answer 2

the gene or chromosome that results from a mutational process

Question 2

mutant

Answer 2

a mutant is the organism or cell whose changed phenotype is attributed to a
mutation

Question 3

General Types of mutation

Answer 3

1. Gene mutation = the allele of a gene changes (this chapter)
2. Chromosome mutation = segments of chromosomes, whole chromosomes, or
   entire sets of chromosomes change

Question 4

What does wild type (wt) mean?

Answer 4

Wild type is an arbitrary standard for what
“normal” is for an organism. Please remember that what is considered wild type today
may have been a mutant in the evolutionary past.

Question 5

Direction of the mutation

Answer 5

Forward mutations are changes away from the wt
2. Reverse mutations (reversions) are changes from the mutant allele back to the
wt allel

Question 6

Mechanisms for gene mutation

Answer 6

1. Errors in DNA replication
2. Errors in DNA repair
3. Environmental mutagen causes DNA damage that is not repaired correctly
4. Transposons and insertion sequences (a mobile DNA elements that can move
   from one location in the chromosome to another; the element may “jump” into a
   gene thereby mutating it)

Question 7

Why study gene mutation?

Answer 7

1. Variants in genes (which are caused by mutations) are needed to study the
   transmission of traits
2. Mutations can tell the researcher about the function of a gene product in a
   biological system
3. Mutations are the basis for cancer and other genetic diseases
4. Gene mutations serve as the source for most alleles in a population and is
   therefore the origin of genetic variation within a population
5. Mutations drive evolution: mutations are the raw material upon which natural
   selection acts

Question 8

Classification of mutations: Point of origin

Answer 8

Somatic mutations
a) mutations that are in the somatic tissues of the body
b) mutations are NOT transmitted to progeny
c) the extent of the phenotypic effect depends upon whether the mutation
is dominant or recessive (dominant mutations generally have a greater
effect)
d) the extent of the phenotypic effect depends upon whether it occurs
early or late in development (early arising mutations have a greater effect)
e) sectoring phenotypes may be seen when the mutation occurs during
embryonic development
f) cancer caused by somatic mutations

Germinal mutations
a) mutations that are in the germ tissues of the body
b) mutations MAY BE transmitted to progeny
c) dominant mutations are seen in first generation after the mutation
occurs
d) if a female gamete containing an X-linked mutation is fertilized, the
males will show the mutant phenotype
e) recessive mutations will only be seen upon the chance mating with an
individual carrying the recessive allele too; thus, the recessive mutation
may remain hidden for many generations

Question 9

Germinal mutations

Answer 9

a) mutations that are in the germ tissues of the body
b) mutations MAY BE transmitted to progeny
c) dominant mutations are seen in first generation after the mutation
occurs
d) if a female gamete containing an X-linked mutation is fertilized, the
males will show the mutant phenotype
e) recessive mutations will only be seen upon the chance mating with an
individual carrying the recessive allele too; thus, the recessive mutation
may remain hidden for many generations

Question 10

Somatic mutations

Answer 10

a) mutations that are in the somatic tissues of the body
b) mutations are NOT transmitted to progeny
c) the extent of the phenotypic effect depends upon whether the mutation
is dominant or recessive (dominant mutations generally have a greater
effect)
d) the extent of the phenotypic effect depends upon whether it occurs
early or late in development (early arising mutations have a greater effect)
e) sectoring phenotypes may be seen when the mutation occurs during
embryonic development
f) cancer caused by somatic mutations

Question 11

Classification of mutations:
Phenotypic effects

Answer 11

1. Morphological mutations are mutations that affect the outwardly visible
   properties of an organism (i.e. curly ears in cats)
2. Lethal mutations are mutations that affect the viability of the organism (i.e.
   Manx cat).
3. Conditional mutations are mutations in which the mutant allele causes the
   mutant phenotype only in certain environments (called the restrictive condition).
   In the permissive condition, the phenotype is no longer mutant. (i.e. Siamese cat
   – mutant allele causes albino phenotype at the restrictive temperature of most of
   the cat body but not at the permissive temperature in the extremities where the
   body temperatures is lower).
4. Biochemical mutations are mutations that may not be visible or affect a
   specific morphological characteristic but may have a general affect on the ability
   to grow or proliferate.
   a) Most microorganisms are prototrophs which means that they can grow
   on a simple growth medium including an energy source and inorganic
   salts. Biochemical mutations include those that affect proteins or enzymes
   required to grow on various nutrients or to synthesize various components.
   Thus, these mutations cause the microorganisms to become auxotrophs
   (they must be supplied with additional nutrients if they are to grow). For
   example, the bacterium Escherichia coli does NOT require the amino acid
   tryptophan for growth because they can synthesize tryptophan. However,
   there are E. coli mutants that have mutations in the trp genes. These
   mutants are auxotrophic for tryptophan, and tryptophan must be added to
   the nutrient medium for growth.
   b) Humans can also have biochemical mutations (also called inborn
   errors in metabolism). Such examples include hemophilia,
   phenylketonuria, and galactosemia

Question 12

1. Morphological mutations

Answer 12

are mutations that affect the outwardly visible
properties of an organism (i.e. curly ears in cats)

Question 13

Lethal mutations

Answer 13

are mutations that affect the viability of the organism (i.e.
Manx cat)

Question 14

Conditional mutations

Answer 14

Conditional mutations are mutations in which the mutant allele causes the
mutant phenotype only in certain environments (called the restrictive condition).
In the permissive condition, the phenotype is no longer mutant. (i.e. Siamese cat
– mutant allele causes albino phenotype at the restrictive temperature of most of
the cat body but not at the permissive temperature in the extremities where the
body temperatures is lower).

Question 15

Biochemical mutations

Answer 15

Biochemical mutations are mutations that may not be visible or affect a
specific morphological characteristic but may have a general affect on the ability
to grow or proliferate.
a) Most microorganisms are prototrophs which means that they can grow
on a simple growth medium including an energy source and inorganic
salts. Biochemical mutations include those that affect proteins or enzymes
required to grow on various nutrients or to synthesize various components.
Thus, these mutations cause the microorganisms to become auxotrophs
(they must be supplied with additional nutrients if they are to grow). For
example, the bacterium Escherichia coli does NOT require the amino acid
tryptophan for growth because they can synthesize tryptophan. However,
there are E. coli mutants that have mutations in the trp genes. These
mutants are auxotrophic for tryptophan, and tryptophan must be added to
the nutrient medium for growth.
b) Humans can also have biochemical mutations (also called inborn
errors in metabolism). Such examples include hemophilia,
phenylketonuria, and galactosemia

Question 16

Loss of function mutations

Answer 16

are those that destroy the function of the gene
product. Many times in diploid organisms, these are recessive mutations because
the other wild type allele still encodes a functional gene product. However, it is
possible to have a dominant loss of function mutation in which the mutant gene
product interferes with the activity of the gene product from the wild type allele

Question 17

Null mutation =

Answer 17

loss of function mutation where gene product is
completely inactive

Question 18

Leaky mutation =

Answer 18

loss of function mutation where gene product is not
completely inactive (partially active still)

Question 19

Gain of function mutations

Answer 19

are those that produce a new function for the gene
product. Gain of function mutations are dominant.

Question 20

Mutation frequency =

Answer 20

of times mutation appears in the population / # of
individuals in the population where a population can be bacterial cells, people,
gametes

Question 21

Mutation rate

Answer 21

= # of mutations / unit time where unit time can be per cell
division, cell generation

Question 22

Frequencies of mutations

Answer 22

Mutations are relatively rare.
4. Different genes have different mutation frequencies (Table 7-1)
5. Different organisms have different overall mutation frequencies (Table 7-2

Question 23

Detection of mutations in humans

Answer 23

1. Detection of germinal dominant mutations by human pedigree analysis (shows
   up in the pedigree as the sudden appearance of a novel phenotype)
2. Detection of germinal recessive mutations are more difficult because they
   remain masked by the dominant allele until the union of two heterozygotes
3. Detection of germinal X-linked mutations arising in female gametes appear in
   some of the males in the generation after the mutation occurred.

Question 24

Detection of mutations using the specific-locus test

Answer 24

a system for detecting recessive mutations in diploids. Heterozygote individual for gene(s)A that give phenotype A is crossed with a homozygous recessive individual for gene(s)a that gives phenotype a. The frequency of the mutant phenotype (a) is quantitated.

Question 25

Detection of X-linked mutations in Drosophila using the ClB chromosome

Answer 25

The ClB chromosome is the X chromosome bearing the C allele which prevents crossover, the l allele which is a recessive lethal, and the Bar allele which is a dominant eye mutation

Question 26

Microorganisms

Answer 26

Microorganisms allow for the use of selective systems for mutation detection vs. the screening systems used for higher organisms. A selective system is one in which the experimenter can DEMAND that the only individuals that grow or survive are the ones that have the mutation of interest. On the other hand, a screening system is one in which the experimenter must examine each individual to see if it has the mutation of interest.

Question 27

Mutations and cancer

Answer 27

A. Cancer is a group of diseases characterized by rapid, uncontrolled proliferation of cells within a tissue resulting in the formation of a tumor. Cancer has many causes and phenotypes but the fundamental mechanism underlying all cancers is genetic. B. There are two types of genes that are involved in cancer formation. 1. Tumor suppressor genes are genes that encode a product that normally stops cell division. Mutations in these genes result in uncontrolled activation of cell division and therefore tumor formation. Mutations are generally recessive and thus you need mutations in both alleles to have cancer. A mutation in one allele predisposes the carrier to cancer. a) Rb gene - retinoblastoma (retinal cancer) b) BRCA1 - hereditary breast cancer gene c) p53 gene mutations are found in a variety of cancers including breast, lung, bladder, and colon cancers. Over 1/2 of all cancers are associated with p53. 2. Proto-oncogenes are genes that encode a product that normally controls cell division (kind of like an on/off switch). Mutations in these genes make the gene product permanently in the on position which results in uncontrolled activation of cell division and therefore tumor formation. a) N-ras – neuroblastoma (tumor formed of embryonic ganglion cells), leukemia b) N-myc – neuroblastoma c) man – mammary carcinoma

Question 28

Tumor suppressor genes

Answer 28

1. are genes that encode a product that normally stops cell division. Mutations in these genes result in uncontrolled activation of cell division and therefore tumor formation. Mutations are generally recessive and thus you need mutations in both alleles to have cancer. A mutation in one allele predisposes the carrier to cancer. a) Rb gene - retinoblastoma (retinal cancer) b) BRCA1 - hereditary breast cancer gene c) p53 gene mutations are found in a variety of cancers including breast, lung, bladder, and colon cancers. Over 1/2 of all cancers are associated with p53.

Question 29

Proto-oncogenes are genes that encode a product that normally controls cell division (kind of like an on/off switch). Mutations in these genes make the gene product permanently in the on position which results in uncontrolled activation of cell division and therefore tumor formation. a) N-ras – neuroblastoma (tumor formed of embryonic ganglion cells), leukemia b) N-myc – neuroblastoma c) man – mammary carcinom

Answer 29

Proto-oncogenes are genes that encode a product that normally controls cell division (kind of like an on/off switch). Mutations in these genes make the gene product permanently in the on position which results in uncontrolled activation of cell division and therefore tumor formation. a) N-ras – neuroblastoma (tumor formed of embryonic ganglion cells), leukemia b) N-myc – neuroblastoma c) man – mammary carcinom

Question 30

Proto-oncogenes are genes that encode a product that normally controls cell division (kind of like an on/off switch). Mutations in these genes make the gene product permanently in the on position which results in uncontrolled activation of cell division and therefore tumor formaMutagens in genetic dissectiontion. a) N-ras – neuroblastoma (tumor formed of embryonic ganglion cells), leukemia b) N-myc – neuroblastoma c) man – mammary carci

Answer 30

A. Mutagens are agents that cause mutations at a rate higher than the spontaneous rate. B. Mutagens can be chemical (i.e. cigarette smoke, mustard gas) or radiation (i.e. UV, X-rays,

Question 32

What is a mutation?

Answer 32

A recent and rare change in DNA sequence within a population. ## Footnote Mutations can arise spontaneously or be induced by environmental factors.

Question 33

What is a polymorphism?

Answer 33

When multiple variants exist in a population and neither is clearly the 'normal' or wild-type. ## Footnote Polymorphisms indicate stable variations in a population.

Question 34

What defines co-existing DNA variations?

Answer 34

When none of the sequence variants can be called the wild-type due to their frequency in the population, classified as polymorphisms. ## Footnote This reflects genetic diversity within a population.

Question 35

What are the origins of mutations?

Answer 35

Mutations can be spontaneous or induced. ## Footnote Spontaneous mutations occur naturally, while induced mutations are caused by mutagens.

Question 36

What are the types of mutations?

Answer 36

Mutations may involve: * Substitutions * Deletions * Insertions ## Footnote Each type alters the DNA sequence in different ways.

Question 37

What functional consequences can a mutation lead to?

Answer 37

A mutation can lead to: * Loss of function * Gain of function ## Footnote Loss of function can result in partial or complete inactivation, while gain of function may provide new or enhanced activity.

Question 38

What causes spontaneous mutations?

Answer 38

Natural errors such as: * Base mispairing * Insertions/deletions, especially in repetitive DNA sequences. ## Footnote These errors occur during DNA replication.

Question 39

What triggers induced mutations?

Answer 39

Induced mutations are triggered by: * DNA damage * Misrepair * Sequence interruption ## Footnote Induced mutations can result from chemical, physical, or biological mutagens.

Question 40

How can mutagenesis be used for gene identification?

Answer 40

By inducing mutations and observing phenotypes, researchers can link mutations to specific genes and pathways. ## Footnote This helps in understanding gene functions and interactions.

Question 41

What are transposable elements (TEs)?

Answer 41

Also called 'jumping genes', TEs are dynamic parts of the genome that contribute to genetic variation and evolution. ## Footnote TEs can move within the genome, affecting gene expression.

Question 42

What are the limits of mutant screening?

Answer 42

Challenges include: * Silent mutations (no phenotype) * Genetic redundancy (multiple genes compensate) * Embryonic lethality (mutation kills embryo) ## Footnote These factors make it difficult to identify and study mutations.

Question 43

What is gene mutation convergence?

Answer 43

Mutations in different genes may cause the same phenotype due to interaction in the same pathway. ## Footnote This phenomenon complicates the understanding of genetic interactions.

Question 44

What is complementation testing?

Answer 44

A method to determine whether two mutations affect the same gene (allelic) or different genes (non-allelic). ## Footnote This testing is crucial for genetic mapping and understanding gene function.

Question 45

What is a mutation in genetic terms?

Answer 45

A recent and rare DNA sequence change in a population. ## Footnote Mutations can contribute to genetic diversity and evolution.

Question 46

What is a polymorphism?

Answer 46

A variation in DNA sequence where neither variant is a clear wild-type. ## Footnote Polymorphisms are often common in populations.

Question 47

What are the two main origins of mutations?

Answer 47

Spontaneous errors and induced mutations from mutagens. ## Footnote Spontaneous mutations occur naturally, while induced mutations result from external factors.

Question 48

Name three types of mutations based on structural change.

Answer 48

* Substitution * Deletion * Insertion ## Footnote Each type of mutation affects the DNA sequence differently.

Question 49

What are the two functional outcomes of mutations?

Answer 49

* Loss of function * Gain of function (possibly new function) ## Footnote Gain of function mutations can lead to novel traits or characteristics.

Question 50

What typically causes spontaneous mutations?

Answer 50

Natural DNA replication errors, base mispairing, or insertions/deletions in repetitive sequences. ## Footnote These errors can occur during cell division.

Question 51

How are induced mutations caused?

Answer 51

Through exposure to chemical, biological, or physical mutagens. ## Footnote Common mutagens include radiation and certain chemicals.

Question 52

How can researchers use mutagenesis in genetics?

Answer 52

To identify genes related to phenotypes by observing effects of random mutations. ## Footnote This method helps in understanding gene functions and interactions.

Question 53

What are transposable elements?

Answer 53

Mobile DNA sequences that are abundant and promote genetic diversity and evolution. ## Footnote They can move within the genome and affect gene expression.

Question 54

What limits mutant screening efficiency?

Answer 54

* Silent mutations * Redundancy * Embryonic lethality ## Footnote These factors can obscure the effects of mutations during analysis.

Question 55

Can different gene mutations produce the same phenotype?

Answer 55

Yes, if they affect the same pathway or function. ## Footnote This phenomenon illustrates the complexity of genetic interactions.

Question 56

What does complementation testing reveal?

Answer 56

Whether mutations are in the same gene (allelic) or different genes (non-allelic). ## Footnote This testing is crucial for understanding genetic relationships.

Question 57

What is a mutation?

Answer 57

A permanent change in the DNA sequence. ## Footnote Mutations can occur in coding or non-coding regions and may affect gene function, regulation, or be silent.

Question 58

What is a mutant?

Answer 58

An organism or cell that carries a mutation. ## Footnote Mutants may display a different phenotype compared to the wild-type.

Question 59

What is a polymorphism in genetics?

Answer 59

A common genetic variation present in at least 1% of the population. ## Footnote Polymorphisms are typically harmless and stable.

Question 60

What is an insertion mutation?

Answer 60

A mutation involving the addition of one or more nucleotides into the DNA sequence.

Question 61

What is a deletion mutation?

Answer 61

A mutation where one or more nucleotides are lost from the DNA sequence.

Question 62

What happens in a substitution mutation?

Answer 62

A single base is replaced by another. ## Footnote Substitution mutations can be silent, missense, or nonsense.

Question 63

What is a mutagen?

Answer 63

Any physical, chemical, or biological agent that increases the rate of mutation.

Question 64

What are DNA replication errors?

Answer 64

Mistakes during DNA copying, such as mispairing of bases, which can cause mutations.

Question 65

What is strand slippage?

Answer 65

A replication error where the DNA polymerase slips, especially in repetitive sequences, leading to insertions or deletions.

Question 66

What is a biological mutagen?

Answer 66

A living agent that causes mutations, e.g., viruses inserting into the genome.

Question 67

What is a chemical mutagen?

Answer 67

A compound that reacts with DNA to cause mutations (e.g., EMS, ethidium bromide).

Question 68

What is a physical mutagen?

Answer 68

Physical factors like UV light or ionizing radiation that damage DNA and cause mutations.

Question 69

What is mispairing in DNA replication?

Answer 69

A replication error where non-complementary bases are incorrectly paired (e.g., A with C instead of T).

Question 70

What is a DNA loop in replication?

Answer 70

A bulge that forms when the DNA strand misaligns during replication or repair.

Question 71

What is an SSR (Simple Sequence Repeat)?

Answer 71

Repeating sequences of 1–6 base pairs, prone to strand slippage and mutation.

Question 72

What is an insertional mutagen?

Answer 72

A mutation caused by DNA insertion (like a transposon) that disrupts gene function. ## Footnote Insertional mutagens can lead to various genetic disorders or phenotypic changes in organisms.

Question 73

What are Class I and Class II transposons?

Answer 73

Class I: retrotransposons (copy-paste); Class II: DNA transposons (cut-paste). ## Footnote Class I transposons move via an RNA intermediate, while Class II transposons move directly as DNA.

Question 74

What is a transposon?

Answer 74

A mobile DNA sequence that can move to new genomic locations. ## Footnote Transposons can disrupt genes and contribute to genetic diversity.

Question 75

How do retrotransposons move?

Answer 75

Via RNA intermediate and reverse transcription into DNA. ## Footnote This process is critical for the replication of retrotransposons within the genome.

Question 76

What does reverse transcriptase do?

Answer 76

Converts RNA back into DNA. ## Footnote Reverse transcriptase is essential for the lifecycle of retroviruses, such as HIV.

Question 77

What is the role of transposase?

Answer 77

Cuts and pastes DNA transposons during transposition. ## Footnote Transposase is crucial for the movement of Class II transposons.

Question 78

What is a non-autonomous transposon?

Answer 78

A transposon that needs enzymes from another element to move. ## Footnote Non-autonomous transposons often rely on nearby autonomous transposons for their mobility.

Question 79

What is an autonomous transposon?

Answer 79

A self-sufficient transposon that produces its own transposase. ## Footnote Autonomous transposons can independently move within the genome.

Question 80

What are SINE, LINE, and Alu elements?

Answer 80

Repetitive mobile DNA elements; Alu is a common SINE. ## Footnote SINEs are typically shorter than LINEs and play roles in genomic evolution.

Question 81

What is a P-element?

Answer 81

A Drosophila transposon used for genetic manipulation. ## Footnote P-elements are widely utilized in genetic research and biotechnological applications.

Question 82

What is T-DNA?

Answer 82

DNA from Agrobacterium used to genetically modify plants. ## Footnote T-DNA is a key component in plant transformation techniques.

Question 83

What is copy-and-paste transposition?

Answer 83

The transposon is duplicated and inserted elsewhere. ## Footnote This mechanism is characteristic of retrotransposons.

Question 84

What is cut-and-paste transposition?

Answer 84

The transposon is excised and reinserted in a new location. ## Footnote This is a common mechanism for DNA transposons.

Question 85

What is an alkylation agent?

Answer 85

A chemical that adds alkyl groups to DNA, causing mutations. ## Footnote Alkylation agents can lead to various types of DNA damage and mutagenesis.

Question 86

What is EMS?

Answer 86

Ethyl Methanesulfonate, an alkylating mutagen that causes base substitutions. ## Footnote EMS is commonly used in laboratory settings to induce mutations for research purposes.

Question 87

What is an intercalating agent?

Answer 87

A chemical that slips between DNA base pairs, distorting the double helix and causing insertions/deletions during replication. ## Footnote Example: ethidium bromide.

Question 88

What is benzopyrene?

Answer 88

A potent carcinogen found in tobacco smoke that forms bulky DNA adducts, leading to mutations.

Question 89

What does carcinogenic mean?

Answer 89

Any substance or agent capable of causing cancer by inducing mutations or disrupting cellular regulation.

Question 90

What is ethidium bromide used for?

Answer 90

It is commonly used to stain DNA and is also a mutagen.

Question 91

What is a thymine dimer?

Answer 91

A type of DNA damage caused by UV radiation where two adjacent thymine bases covalently bond, distorting DNA structure.

Question 92

What is a mutant screen?

Answer 92

A technique used to identify individuals with mutations in a specific gene or pathway based on phenotype.

Question 93

What is a loss-of-function mutation?

Answer 93

A mutation that results in a gene product with reduced or no function.

Question 94

What is a gain-of-function mutation?

Answer 94

A mutation that leads to a gene product with enhanced, new, or unregulated function.

Question 95

What is an amorph mutation?

Answer 95

A type of loss-of-function mutation where the gene product is completely inactive.

Question 96

What is a null mutation?

Answer 96

A mutation that completely abolishes gene function—no protein made or protein is nonfunctional.

Question 97

What is a hypomorph mutation?

Answer 97

A mutation that causes partial loss of gene function—reduced expression or activity.

Question 98

What is a hypermorph mutation?

Answer 98

A mutation that results in increased gene function or activity.

Question 99

What is a neomorph mutation?

Answer 99

A mutation that gives the gene product a new, abnormal function not seen in the wild-type.

Question 100

What is a dominant negative mutation?

Answer 100

A mutant protein that interferes with the normal function of the wild-type protein, often forming nonfunctional complexes.

Question 101

What are somatic cells?

Answer 101

All body cells excluding gametes; mutations here are not heritable but can lead to diseases like cancer.

Question 102

What are germline cells?

Answer 102

Reproductive cells that pass mutations to the next generation. ## Footnote Germline cells include sperm and eggs.

Question 103

What is a silent mutation?

Answer 103

A base change that does not alter the amino acid sequence. ## Footnote This is due to the redundancy of the genetic code.

Question 104

What is an inter-genic region?

Answer 104

DNA located between genes, often regulatory. ## Footnote Mutations in these regions may affect gene regulation without altering protein coding.

Question 105

What is redundancy in genetics?

Answer 105

Backup or overlapping gene functions that mask mutations. ## Footnote This means that a mutation in one gene may not show an effect because other genes can compensate.

Question 106

What is an essential gene?

Answer 106

A gene necessary for organismal survival. ## Footnote Mutations in essential genes usually lead to embryonic lethality if not compensated.

Question 107

What is a recessive lethal allele?

Answer 107

A lethal mutation only when homozygous. ## Footnote This means that the organism must have two copies of the mutant allele for it to cause death.

Question 108

What does complementation testing determine?

Answer 108

Whether two mutations are in the same gene or different ones. ## Footnote This is done by combining mutations in a diploid cell or organism.

Question 109

What's the difference between allelic and non-allelic mutations?

Answer 109

Allelic = same gene; Non-allelic = different genes. ## Footnote Allelic mutations refer to different mutations within the same gene.

Question 110

What do cM₀, M₁, and M₂ refer to?

Answer 110

Generations in mutagenesis: cM₀ (treated), M₁ (1st), M₂ (2nd, screened). ## Footnote This notation is used to track generations in genetic studies.

Question 111

What is lethality in genetics?

Answer 111

A mutation that causes death. ## Footnote This can occur during development or later in life.

Question 112

What does allelic mean?

Answer 112

Mutations in the same gene. ## Footnote These mutations can be different forms of the same genetic locus.

Question 113

What does non-allelic mean?

Answer 113

Mutations in different genes. ## Footnote These mutations may still produce similar phenotypes.

Question 114

What is a complementation group?

Answer 114

A set of mutations that fail to complement each other — same gene. ## Footnote All mutations in this group affect the same gene's function.

Question 115

What is CFTR?

Answer 115

A gene mutated in cystic fibrosis; encodes a chloride channel. ## Footnote This gene is crucial for fluid regulation in various tissues.

Question 116

What causes cystic fibrosis?

Answer 116

Mutations in the CFTR gene leading to thick mucus buildup. ## Footnote This buildup occurs in the lungs and other organs, causing various health issues.

Question 117

What is the ΔF508 (Phe508del) mutation?

Answer 117

A deletion of phenylalanine at position 508 in CFTR, leading to cystic fibrosis.

Question 118

How does ΔF508 cause disease?

Answer 118

The CFTR protein misfolds and is destroyed before reaching the cell membrane.

Question 119

What is Kalydeco (Ivacaftor)?

Answer 119

A drug that enhances function of some mutant CFTR proteins in cystic fibrosis patients.

Question 120

What does fidelity refer to in the context of DNA?

Answer 120

Fidelity refers to how well DNA maintains its sequence during replication from one generation to the next.

Question 121

What is a mutation?

Answer 121

A mutation is a change in the DNA sequence.

Question 122

What term is used for an individual affected by a mutation that alters their phenotype?

Answer 122

Mutant

Question 123

True or False: A change in DNA sequence is not considered a mutation unless it visibly affects traits.

Answer 123

False

Question 124

How do mutations typically arise?

Answer 124

Mutations can arise naturally and are typically rare.

Question 125

What is a polymorphism?

Answer 125

A polymorphism is a naturally occurring variation in DNA that is not clearly abnormal and occurs at a relatively high frequency in the population (>1%).

Question 126

How do polymorphisms differ from mutations?

Answer 126

Polymorphisms are common and often harmless, while mutations are typically rare and can be harmful.

Question 127

Fill in the blank: Polymorphisms are referred to instead of mutations because many traits don’t have a single _______.

Answer 127

[normal] type

Question 128

What common biochemical processes give rise to both mutations and polymorphisms?

Answer 128

Replication errors and DNA damage.

Question 129

What does the term polymorphism avoid suggesting?

Answer 129

That one allele is 'normal' or 'abnormal'.

Question 130

Provide an example of a mutation.

Answer 130

A DNA change that causes a disease like cancer.

Question 131

Provide an example of a polymorphism.

Answer 131

A DNA change that explains normal variation, like red vs. black hair.

Question 132

What are molecular markers often used for in genetics research?

Answer 132

To track inheritance, identify genes, and study populations.

Question 133

What does Figure 4.0.1 illustrate?

Answer 133

Mouse embryos, showing wild-type (normal development) and a mutant embryo with abnormal cranium development due to a gene mutation.

Question 134

What does the fidelity of DNA refer to?

Answer 134

Its ability to accurately pass genetic information from one generation to the next.

Question 135

What is a mutation?

Answer 135

A change in the DNA sequence that may or may not affect phenotype.

Question 136

What defines a mutant?

Answer 136

An individual whose phenotype has been altered due to a mutation.

Question 137

What is a polymorphism?

Answer 137

A common DNA sequence variant (>1% frequency) not considered abnormal.

Question 138

What is the frequency threshold for a DNA change to be considered a polymorphism?

Answer 138

Greater than 1% in the population.

Question 139

Can mutations and polymorphisms arise from the same biochemical processes?

Answer 139

Yes, both can result from errors like base mispairing or DNA damage.

Question 140

Why do we use the term polymorphism instead of mutation in some cases?

Answer 140

To avoid implying that one allele is abnormal or inferior.

Question 141

Give an example of a mutation.

Answer 141

A DNA change that causes cancer.

Question 142

Give an example of a polymorphism.

Answer 142

A DNA variant that results in red hair instead of black.

Question 143

What role do polymorphisms play in genetic research?

Answer 143

They serve as molecular markers for studying inheritance and population genetics.

Question 144

What are mutations?

Answer 144

Changes in the DNA sequence ## Footnote Mutations can occur in several structural forms and result from different sources.

Question 145

What is a deletion mutation?

Answer 145

Loss of one or more base pairs from the DNA sequence ## Footnote Can disrupt gene function by shifting the reading frame or removing essential coding regions.

Question 146

What is an insertion mutation?

Answer 146

Addition of one or more base pairs into the DNA sequence ## Footnote May cause a frameshift mutation, especially if not in multiples of three, leading to incorrect protein translation.

Question 147

What is a substitution mutation?

Answer 147

Replacement of one or more base pairs with different ones ## Footnote Can be silent, missense, or nonsense.

Question 148

Define silent mutation.

Answer 148

No effect on protein ## Footnote A type of substitution mutation.

Question 149

Define missense mutation.

Answer 149

Changes one amino acid ## Footnote A type of substitution mutation.

Question 150

Define nonsense mutation.

Answer 150

Creates a premature stop codon ## Footnote A type of substitution mutation.

Question 151

What are spontaneous mutations?

Answer 151

Occur naturally without external influence ## Footnote Caused by errors during DNA replication or natural biochemical decay.

Question 152

What are induced mutations?

Answer 152

Result from exposure to mutagens ## Footnote May be introduced intentionally or unintentionally.

Question 153

What is a mutagen?

Answer 153

Agents that increase mutation rate ## Footnote Can be biological, chemical, or physical.

Question 154

Give an example of a biological mutagen.

Answer 154

Viruses that integrate into the genome ## Footnote Disrupt genes.

Question 155

Give an example of a chemical mutagen.

Answer 155

Alkylating agents ## Footnote Other examples include intercalating agents and base analogs.

Question 156

Give an example of a physical mutagen.

Answer 156

UV light ## Footnote Causes thymine dimers.

Question 157

Fill in the blank: Mutations can be classified into three structural types: deletion, insertion, and _______.

Answer 157

substitution

Question 158

What is a deletion mutation?

Answer 158

The loss of one or more base pairs from DNA. ## Footnote Deletion mutations can lead to frameshift mutations if they are not in multiples of three base pairs.

Question 159

What is an insertion mutation?

Answer 159

The addition of one or more base pairs into DNA. ## Footnote Insertion mutations can also cause frameshift mutations, altering the reading frame of the genetic code.

Question 160

What is a substitution mutation?

Answer 160

The replacement of one base pair with another in DNA. ## Footnote Substitution mutations can affect protein function depending on the nature of the change.

Question 161

What are the three outcomes of a substitution mutation?

Answer 161

* Silent * Missense * Nonsense ## Footnote Silent mutations do not change the amino acid sequence, missense mutations change one amino acid, and nonsense mutations create a premature stop codon.

Question 162

What is a spontaneous mutation?

Answer 162

A naturally occurring mutation due to internal processes like replication errors. ## Footnote Spontaneous mutations are part of normal cellular processes and can occur at any time.

Question 163

What is an induced mutation?

Answer 163

A mutation caused by external agents known as mutagens. ## Footnote Induced mutations can significantly increase mutation rates compared to spontaneous mutations.

Question 164

What are the three main classes of mutagens?

Answer 164

* Biological * Chemical * Physical ## Footnote Each class of mutagens can cause different types of mutations and have various mechanisms of action.

Question 165

Give an example of a biological mutagen.

Answer 165

A virus inserting into a host genome. ## Footnote Biological mutagens can disrupt normal gene function and lead to diseases.

Question 166

Give an example of a chemical mutagen.

Answer 166

Ethyl methanesulfonate (EMS), which alkylates DNA bases. ## Footnote Chemical mutagens can cause a wide variety of mutations depending on their structure and reactivity.

Question 167

Give an example of a physical mutagen.

Answer 167

Ultraviolet (UV) light that causes thymine dimers. ## Footnote UV light can lead to errors during DNA replication if not properly repaired.

Question 168

What is the role of DNA polymerase during DNA replication?

Answer 168

Typically inserts the correct complementary base and has proofreading mechanisms to catch and correct mistakes.

Question 169

What happens if DNA replication errors are not repaired?

Answer 169

They become permanent mutations passed to daughter cells.

Question 170

What is an example of mispaired bases during DNA replication?

Answer 170

G-T mispairing instead of proper A-T.

Question 171

What can cause mispairing during DNA replication?

Answer 171

* Tautomeric shifts * Chemical modifications like alkylation * Other replication stress factors

Question 172

What occurs if a DNA replication error, such as a G-T pair, is not repaired?

Answer 172

It becomes a permanent point mutation in subsequent generations.

Question 173

What is strand slippage?

Answer 173

A loop forms due to misalignment between the template strand and daughter strand.

Question 174

What happens when the loop is on the template strand during strand slippage?

Answer 174

Bases in the loop may be skipped, leading to a deletion in the new daughter strand.

Question 175

What occurs when the loop is on the daughter strand during strand slippage?

Answer 175

The bases in the loop are re-replicated, causing an insertion.

Question 176

In what types of DNA sequences is strand slippage especially common?

Answer 176

Repetitive sequences.

Question 177

What are Simple Sequence Repeats (SSRs)?

Answer 177

Regions of DNA with repeats of 1–6 base pairs.

Question 178

What is another term for Simple Sequence Repeats (SSRs)?

Answer 178

Microsatellites.

Question 179

Why are SSRs and microsatellites considered mutation hotspots?

Answer 179

Due to strand slippage.

Question 180

What are the characteristics of SSRs and microsatellites?

Answer 180

* Highly polymorphic * Useful in genetic mapping and forensic analysis

Question 181

What is a major biological source of spontaneous mutation?

Answer 181

Errors during DNA replication ## Footnote Spontaneous mutations can arise from various processes, but replication errors are a significant contributor.

Question 182

What happens if a mispaired base is not corrected during replication?

Answer 182

It becomes a permanent mutation in the next generation ## Footnote This can lead to inherited mutations in descendants.

Question 183

What causes base mispairing during replication?

Answer 183

Tautomeric shifts, alkylation, or replication stress ## Footnote These factors can lead to incorrect base pairing, resulting in mutations.

Question 184

What is strand slippage?

Answer 184

A replication error where a loop forms, causing misalignment between template and daughter strands ## Footnote This misalignment can lead to insertions or deletions.

Question 185

What mutation occurs if the loop forms on the template strand during slippage?

Answer 185

A deletion in the daughter strand ## Footnote This results from the daughter strand losing nucleotides due to the misalignment.

Question 186

What mutation occurs if the loop forms on the daughter strand during slippage?

Answer 186

An insertion in the daughter strand ## Footnote This results from the daughter strand gaining additional nucleotides.

Question 187

What are SSRs (Simple Sequence Repeats)?

Answer 187

DNA regions with short, repeated sequences prone to strand slippage ## Footnote SSRs are significant in understanding genetic variation.

Question 188

Why are SSRs also called microsatellites?

Answer 188

Because they are small, repetitive DNA segments useful for genetic analysis ## Footnote The term 'microsatellite' reflects their size and repetitive nature.

Question 189

Why are microsatellites highly polymorphic?

Answer 189

Due to frequent insertions/deletions from strand slippage ## Footnote This polymorphism makes them useful for various genetic studies.

Question 190

What are microsatellites used for in genetics?

Answer 190

Genetic mapping, forensic profiling, and population studies ## Footnote Their variability makes them ideal for these applications.

Question 191

What are insertional mutations?

Answer 191

Mutations resulting from the insertion of foreign DNA into the genome ## Footnote Common sources include viruses, transposable elements, and other mobile DNA segments.

Question 192

What can insertional mutations disrupt?

Answer 192

Coding sequences of genes and regulatory regions ## Footnote Disruption can destroy or alter protein function and affect gene expression.

Question 193

What are gene fusions?

Answer 193

Combining parts of two different genes, potentially forming abnormal or novel proteins.

Question 194

How can insertions occur?

Answer 194

Spontaneously as natural mutations or artificially through experimental methods ## Footnote This distinction is important in genetic research.

Question 195

What is transposon-tagging?

Answer 195

A genetic technique using transposable elements as mutagens to disrupt genes and identify gene function.

Question 196

What is the main use of transposon-tagging?

Answer 196

To study gene roles in model organisms.

Question 197

What is a P Element?

Answer 197

A type of transposable element found in Drosophila, commonly used to induce mutations in labs.

Question 198

What is T-DNA?

Answer 198

A modified DNA element from Agrobacterium tumefaciens used in plants to insert genes and create mutations.

Question 199

True or False: Insertional mutations can only occur through artificial methods.

Answer 199

False.

Question 200

Fill in the blank: Insertional mutations can cause _______ by combining parts of two different genes.

Answer 200

[gene fusions]

Question 201

What is an insertional mutation?

Answer 201

A mutation caused by the insertion of foreign DNA into a genome, disrupting gene function or regulation. ## Footnote Insertional mutations can lead to various genetic disorders or phenotypic changes in organisms.

Question 202

Name two biological agents that can cause insertional mutations.

Answer 202

* Viruses * Transposable elements (transposons) ## Footnote Both agents can integrate their genetic material into host genomes, leading to mutations.

Question 203

What happens when a transposon inserts into a gene's coding region?

Answer 203

It may disrupt the gene, alter its expression, or fuse it with another gene. ## Footnote This can result in loss of function or gain of new functions in the affected genes.

Question 204

Can insertional mutations occur naturally?

Answer 204

Yes, they can occur spontaneously during normal cellular processes. ## Footnote Natural insertional mutations contribute to genetic diversity and evolution.

Question 205

What is transposon-tagging?

Answer 205

A lab technique using transposons to deliberately induce mutations and identify gene functions. ## Footnote This method allows researchers to study gene function by observing the effects of induced mutations.

Question 206

What is the P element used for?

Answer 206

It's a transposable element used as a biological mutagen in Drosophila research. ## Footnote The P element facilitates the study of gene function and regulation in fruit flies.

Question 207

What is T-DNA and where is it used?

Answer 207

T-DNA is a bacterial DNA segment used to mutate plant genes for research. ## Footnote T-DNA is often used in Agrobacterium-mediated transformation to introduce new traits into plants.

Question 208

How do insertional elements affect gene regulation?

Answer 208

By disrupting promoter or enhancer regions, changing when and where genes are expressed. ## Footnote This can lead to altered phenotypes and can be a mechanism for gene expression changes.

Question 209

What is gene fusion in the context of insertional mutations?

Answer 209

The merging of parts of two genes due to DNA insertion, potentially creating a novel gene product. ## Footnote Gene fusions can result in proteins with new functions, which may have implications in diseases like cancer.

Question 210

What are Transposable Elements (TEs)?

Answer 210

Segments of DNA that can move from one location to another within the genome ## Footnote Also called mobile genetic elements or jumping genes

Question 211

What is the process of movement for Transposable Elements called?

Answer 211

Transposition

Question 212

In which organisms are Transposable Elements present?

Answer 212

Almost all organisms

Question 213

What are the important roles of Transposable Elements?

Answer 213

* Gene disruption (causing mutation) * Phenotypic variation * Evolutionary change

Question 214

How do TEs cause mutations?

Answer 214

By inserting themselves into coding or regulatory regions

Question 215

What can the disruption caused by TEs do?

Answer 215

* Knock out gene function * Create new gene combinations * Cause instability in the genome

Question 216

What are the two major classes of TEs in Eukaryotes?

Answer 216

* Class I TEs: Retrotransposons * Class II TEs: DNA Transposons

Question 217

What is the mechanism of Class I TEs?

Answer 217

Copy-and-paste (original copy remains, new copy is inserted)

Question 218

What enzymes are involved in Class I TEs?

Answer 218

* Reverse transcriptase * Integrase

Question 219

What is an example of Class I TEs?

Answer 219

* LINEs * SINEs * Alu

Question 220

What is the mechanism of Class II TEs?

Answer 220

Cut-and-paste (original copy is removed and reinserted)

Question 221

What enzyme is used by Class II TEs?

Answer 221

Transposase

Question 222

What are Autonomous TEs?

Answer 222

TEs that encode all necessary enzymes for their own transposition

Question 223

What are Non-autonomous TEs?

Answer 223

TEs that rely on enzymes from other TEs

Question 224

What percentage of the human genome consists of TEs?

Answer 224

Nearly 45%

Question 225

Which class of TEs predominates in the human genome?

Answer 225

Class I elements (retrotransposons)

Question 226

How many times is Alu, a SINE element, found in the human genome?

Answer 226

>1 million times

Question 227

How do TEs compare in number to actual protein-coding genes in the human genome?

Answer 227

TEs far outnumber actual protein-coding genes (only ~21,000 genes)

Question 228

How can cut-and-paste Class II TEs lead to increases in copy number?

Answer 228

Through DNA repair using a template that still contains the TE

Question 229

What are transposable elements (TEs)?

Answer 229

Mobile DNA segments that can move within the genome, also called jumping genes. ## Footnote TEs can play significant roles in genome evolution and diversity.

Question 230

What is transposition?

Answer 230

The process of TEs moving from one genomic location to another. ## Footnote This can lead to genetic variation and mutations.

Question 231

How can TEs cause mutations?

Answer 231

By inserting into coding or regulatory regions, disrupting gene expression or function. ## Footnote This disruption can lead to various phenotypic effects.

Question 232

What is the difference between Class I and Class II TEs?

Answer 232

Class I uses an RNA intermediate (copy-paste), Class II uses direct DNA movement (cut-paste). ## Footnote This fundamental difference affects their mechanisms of transposition.

Question 233

What enzymes do Class I elements use?

Answer 233

Reverse transcriptase and integrase. ## Footnote These enzymes are crucial for the replication of RNA intermediates.

Question 234

What enzyme do Class II elements use?

Answer 234

Transposase. ## Footnote Transposase facilitates the cut-and-paste mechanism of transposition.

Question 235

What is an autonomous TE?

Answer 235

A TE that encodes all proteins required for its own transposition. ## Footnote Autonomous TEs can function independently in the genome.

Question 236

What is a non-autonomous TE?

Answer 236

A TE that requires help from another TE to transpose. ## Footnote Non-autonomous TEs depend on the enzymes produced by autonomous TEs.

Question 237

What is the most abundant SINE in humans?

Answer 237

Alu element, found over 1 million times. ## Footnote Alu elements are a significant component of the human genome.

Question 238

How much of the human genome is made of TEs?

Answer 238

About 45%. ## Footnote TEs contribute to a large portion of the genomic architecture.

Question 239

What are LINEs and SINEs?

Answer 239

Families of Class I retrotransposons in the human genome. ## Footnote LINEs (Long Interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements) are key players in genomic structure.

Question 240

How can Class II elements increase in copy number despite cut-paste?

Answer 240

If the excised site is repaired with a template that includes the TE. ## Footnote This can lead to an increase in the overall number of TEs in the genome.

Question 241

What do TEs greatly increase in genomes?

Answer 241

The total DNA content of genomes ## Footnote TEs can copy themselves and insert into various locations, contributing to genome size.

Question 242

What was once thought to be 'junk DNA' is now known to be?

Answer 242

TEs ## Footnote This highlights the functional significance of TEs in the genome.

Question 243

How can TEs disrupt gene function?

Answer 243

By inserting into coding sequences and regulatory regions ## Footnote This affects both protein structure and gene expression levels.

Question 244

What process leads to gene duplication via transposition?

Answer 244

Transposition ## Footnote Neighboring chromosomal regions may be carried along with the TE during this process.

Question 245

What can happen to duplicated genes?

Answer 245

They can evolve separately and gain new functions ## Footnote This is a major mechanism in evolutionary innovation.

Question 246

What can TE excision and reinsertion cause?

Answer 246

Break chromosomes and cause errors during repair ## Footnote This can result in rearrangements, deletions, or fusions of chromosomes.

Question 247

What meiotic errors can repetitive TEs cause?

Answer 247

Homologous chromosomes can misalign ## Footnote This can lead to unequal crossing-over, resulting in duplication or deletion.

Question 248

What happens during unequal crossing-over?

Answer 248

One chromosome gains extra material, the other loses material ## Footnote This leads to genetic imbalances in the offspring.

Question 249

What is the conclusion regarding TEs?

Answer 249

TEs are not junk DNA ## Footnote They are recognized as genomic innovators and drivers of evolution.

Question 250

True or False: TEs are considered useless in the genome.

Answer 250

False ## Footnote TEs are now acknowledged for their important roles in mutation, duplication, and rearrangement.

Question 251

How do TEs affect genome size?

Answer 251

They expand genome size by copying and inserting themselves into new locations. ## Footnote Transposable elements (TEs) can increase the amount of DNA in a genome through their replication and insertion mechanisms.

Question 252

Can TEs still be considered 'junk DNA'?

Answer 252

No, they play important roles in genome structure, evolution, and regulation. ## Footnote TEs are now recognized for their contributions to genetic diversity and regulatory functions.

Question 253

What happens when TEs disrupt coding or regulatory regions?

Answer 253

They can inactivate or misregulate genes, leading to mutations. ## Footnote Disruption by TEs can have significant impacts on gene expression and functionality.

Question 254

How can TEs cause gene duplication?

Answer 254

By accidentally carrying adjacent DNA during transposition. ## Footnote This process can lead to the creation of multiple gene copies, which can evolve independently.

Question 255

What is the evolutionary importance of gene duplication?

Answer 255

It allows one gene copy to mutate and gain new functions. ## Footnote Gene duplication is a key mechanism in the evolution of new traits and functions in organisms.

Question 256

How do TEs cause chromosome rearrangements?

Answer 256

By breaking DNA during excision/integration and causing faulty rejoining. ## Footnote These rearrangements can have significant effects on genome organization and function.

Question 257

What is unequal crossing-over?

Answer 257

Misaligned pairing of homologous chromosomes during meiosis, often due to repetitive TEs, causing duplication/deletion. ## Footnote This process can lead to genetic diversity but may also result in harmful mutations.

Question 258

Why do repeated TEs increase the risk of meiotic error?

Answer 258

Because they can cause mispairing between homologous chromosomes. ## Footnote The presence of repetitive sequences can lead to genomic instability during cell division.

Question 259

What do transposable elements (TEs) do to the genome?

Answer 259

TEs actively shape the genome and drive evolutionary change ## Footnote TEs increase genome size and influence gene function.

Question 260

How do transposable elements contribute to genome expansion?

Answer 260

By inserting copies of themselves throughout the genome ## Footnote This can lead to larger genomes in some organisms compared to others with the same gene count.

Question 261

What are the effects of transposable elements inserting into a gene's coding or regulatory region?

Answer 261

* Block gene expression * Alter protein coding sequences * Cause disease or phenotypic change ## Footnote Disruption can lead to various genetic disorders.

Question 262

What is gene duplication in the context of transposable elements?

Answer 262

When TEs accidentally carry nearby DNA and insert it elsewhere ## Footnote This can lead to the evolution of new gene functions.

Question 263

What can happen during chromosomal breakage and rearrangement caused by TEs?

Answer 263

* Break chromosomes * Cause rearrangements (inversions or translocations) * Cause deletions if strand rejoining is incorrect ## Footnote These alterations can significantly impact genetic stability.

Question 264

What is the significance of unequal crossing-over during meiosis related to TEs?

Answer 264

It leads to one chromosome gaining extra material (duplication) while the other loses material (deletion) ## Footnote This occurs due to misalignment of homologous chromosomes.

Question 265

What was the former perception of transposable elements and how has it changed?

Answer 265

They were once considered 'junk DNA', but are now seen as: * Evolutionary drivers * Sources of genomic innovation * Agents of diversity and adaptation ## Footnote This shift in understanding highlights their importance in evolution.

Question 266

What is Forward Genetics?

Answer 266

An approach used to identify which genes control specific biological traits ## Footnote It involves randomly inducing mutations, screening for altered phenotypes, and investigating mutated genes.

Question 267

What are the steps involved in Forward Genetics?

Answer 267

1. Randomly induce mutations in a large population of organisms 2. Screen for individuals with altered phenotypes 3. Investigate which gene(s) are mutated to cause the observed phenotype ## Footnote These steps help in linking genes to specific traits.

Question 268

How are mutations introduced in Forward Genetics?

Answer 268

Using mutagens (chemical, biological, or physical agents) to cause random mutations across the genome ## Footnote This creates a diverse pool of mutants with potential disruptions in different genes.

Question 269

What is Mutant Screening?

Answer 269

A process where researchers observe a population for individuals with abnormal traits and select those mutants to identify the responsible genes ## Footnote This is a critical step in linking phenotypes to specific genetic mutations.

Question 270

What model organism is commonly used in Forward Genetics studies?

Answer 270

Drosophila melanogaster (fruit fly) ## Footnote This organism is favored due to its simple genetics and ease of manipulation.

Question 271

What example is provided for learning and memory research in Drosophila?

Answer 271

Flies were mutagenized and screened for larvae unable to learn, specifically failing to associate a smell with a painful electric shock ## Footnote This indicates defective genes involved in learning and memory.

Question 272

What broader relevance do the genes identified through forward genetic screens have?

Answer 272

They may help scientists understand cognitive processes and neurodegenerative diseases like Alzheimer’s disease ## Footnote Insights from simple organisms can inform human biology due to conserved molecular machinery.

Question 273

True or False: Forward Genetics can provide insights into human biology.

Answer 273

True ## Footnote The conservation of molecular mechanisms allows findings in model organisms to be relevant to humans.

Question 274

Fill in the blank: Forward Genetics works by inducing _______ in a population of organisms.

Answer 274

[random mutations]

Question 275

What is Forward Genetics?

Answer 275

An approach used to identify which genes control specific biological traits ## Footnote It involves randomly inducing mutations, screening for altered phenotypes, and investigating mutated genes.

Question 276

What are the steps involved in Forward Genetics?

Answer 276

1. Randomly induce mutations in a large population of organisms 2. Screen for individuals with altered phenotypes 3. Investigate which gene(s) are mutated to cause the observed phenotype ## Footnote These steps help in linking genes to specific traits.

Question 277

How are mutations introduced in Forward Genetics?

Answer 277

Using mutagens (chemical, biological, or physical agents) to cause random mutations across the genome ## Footnote This creates a diverse pool of mutants with potential disruptions in different genes.

Question 278

What is Mutant Screening?

Answer 278

A process where researchers observe a population for individuals with abnormal traits and select those mutants to identify the responsible genes ## Footnote This is a critical step in linking phenotypes to specific genetic mutations.

Question 279

What model organism is commonly used in Forward Genetics studies?

Answer 279

Drosophila melanogaster (fruit fly) ## Footnote This organism is favored due to its simple genetics and ease of manipulation.

Question 280

What example is provided for learning and memory research in Drosophila?

Answer 280

Flies were mutagenized and screened for larvae unable to learn, specifically failing to associate a smell with a painful electric shock ## Footnote This indicates defective genes involved in learning and memory.

Question 281

What broader relevance do the genes identified through forward genetic screens have?

Answer 281

They may help scientists understand cognitive processes and neurodegenerative diseases like Alzheimer’s disease ## Footnote Insights from simple organisms can inform human biology due to conserved molecular machinery.

Question 282

True or False: Forward Genetics can provide insights into human biology.

Answer 282

True ## Footnote The conservation of molecular mechanisms allows findings in model organisms to be relevant to humans.

Question 283

Fill in the blank: Forward Genetics works by inducing _______ in a population of organisms.

Answer 283

[random mutations]

Question 284

What is forward genetics?

Answer 284

A strategy to identify genes by inducing mutations and screening for phenotypic changes.

Question 285

What is mutant screening?

Answer 285

The process of searching for organisms with abnormal traits to identify the underlying genetic cause.

Question 286

How are mutations introduced in forward genetics?

Answer 286

Randomly, using mutagens such as chemicals or radiation.

Question 287

What organism is commonly used in forward genetic screens?

Answer 287

Drosophila melanogaster (fruit fly).

Question 288

What learning defect was studied in mutant Drosophila larvae?

Answer 288

Inability to associate a specific odor with an electric shock.

Question 289

Why are model organisms useful in genetic screening?

Answer 289

Their genes often function similarly to human genes, making discoveries applicable to human biology.

Question 290

What human disease might benefit from insights gained via forward genetics?

Answer 290

Alzheimer’s disease.

Question 291

What is the ultimate goal of forward genetics?

Answer 291

To discover genes responsible for particular traits or biological processes.

Question 292

What are genetic screens?

Answer 292

Experimental techniques used to identify genes involved in specific biological processes and characterize gene function through observable mutant phenotypes ## Footnote Genetic screens help researchers understand the roles of different genes in various biological contexts.

Question 293

How are genetic screens conducted?

Answer 293

A population is treated with a mutagen, creating random mutations throughout the genome ## Footnote Common mutagens include EMS and radiation.

Question 294

What is the goal of mutating the germline in genetic screens?

Answer 294

To create heritable mutations that can be passed on to offspring ## Footnote Germline mutations occur in egg and sperm precursors.

Question 295

What are germline cells?

Answer 295

Gametes and their precursors; mutations here are heritable ## Footnote Germline mutations can affect future generations.

Question 296

What are somatic cells?

Answer 296

Body cells; mutations are not passed on ## Footnote Somatic mutations affect the individual but not their offspring.

Question 297

How do researchers make mutations observable?

Answer 297

By crossing or mating mutagenized organisms and screening for new, visible phenotypes in the next generation ## Footnote This often involves allowing mutations to become homozygous or hemizygous.

Question 298

What are loss-of-function mutations?

Answer 298

Mutations where the gene product is reduced or absent, usually recessive ## Footnote Types include amorph or null (complete loss) and hypomorph (partial loss).

Question 299

What are gain-of-function mutations?

Answer 299

Mutations that cause overactivity of the gene (hypermorph) or a new function of the protein (neomorph) ## Footnote These mutations may be dominant.

Question 300

What are antimorph (dominant negative) mutations?

Answer 300

Mutant gene products that actively interfere with the normal, wild-type protein, dominant and opposite to wild-type function ## Footnote Antimorphs can disrupt normal biological processes.

Question 301

Fill in the blank: Genetic screens are used to identify genes involved in _______.

Answer 301

[specific biological processes]

Question 302

True or False: Germline mutations are not passed on to offspring.

Answer 302

False

Question 303

What is the goal of a genetic screen?

Answer 303

To identify and study genes based on the phenotypes caused by induced mutations.

Question 304

What is used to induce mutations in genetic screens?

Answer 304

Mutagens like EMS (ethyl methanesulfonate), radiation, or chemical agents.

Question 305

Why are germline mutations important in genetic screens?

Answer 305

Because they are heritable and can be passed to offspring for phenotype analysis.

Question 306

What are somatic mutations?

Answer 306

Mutations in non-reproductive cells; they are not passed to offspring.

Question 307

Why must mutagenized individuals be bred?

Answer 307

To produce homozygous or hemizygous offspring where recessive mutations become visible.

Question 308

What are loss-of-function mutations?

Answer 308

Mutations that reduce or eliminate gene function.

Question 309

What is an amorph or null mutation?

Answer 309

A complete loss-of-function mutation where the gene product is inactive or missing.

Question 310

What is a hypomorph?

Answer 310

A partial loss-of-function mutation with reduced activity of the gene product.

Question 311

What is a gain-of-function mutation?

Answer 311

A mutation that increases the gene product’s activity or creates a new function.

Question 312

What is a hypermorph?

Answer 312

A gain-of-function mutation with overproduction or overactivity of a protein.

Question 313

What is a neomorph?

Answer 313

A gain-of-function mutation that results in a new, abnormal protein function.

Question 314

What is an antimorph mutation?

Answer 314

A dominant negative mutation that blocks or opposes wild-type gene function.

Question 315

Are most mutations from genetic screens dominant or recessive?

Answer 315

Recessive.

Question 316

What is the definition of an Amorph (Null) mutation?

Answer 316

Complete loss-of-function ## Footnote Produces no active product — zero function.

Question 317

What is the effect of an Amorph mutation?

Answer 317

Produces no active product — zero function ## Footnote Often due to gene deletion or a nonfunctional protein.

Question 318

What are the common causes of an Amorph mutation?

Answer 318

* No transcription (gene deletion, regulatory mutation) * A nonfunctional protein (e.g., nonsense mutation) ## Footnote These causes lead to a complete loss of gene function.

Question 319

What is the dominance pattern of an Amorph mutation?

Answer 319

Usually recessive to wild-type ## Footnote Also called a null allele.

Question 320

What is the definition of a Hypomorph mutation?

Answer 320

Partial loss-of-function ## Footnote Produces a weak or reduced function protein.

Question 321

What is the effect of a Hypomorph mutation?

Answer 321

Produces a weak or reduced function protein ## Footnote This results in less effective gene product.

Question 322

What are the common causes of a Hypomorph mutation?

Answer 322

* Less transcription * Protein is produced but is only partially functional ## Footnote This type of mutation is also known as a leaky mutation.

Question 323

What is the dominance pattern of a Hypomorph mutation?

Answer 323

Usually recessive ## Footnote Both amorphs and hypomorphs are usually recessive because one wild-type copy is often haplo-sufficient.

Question 324

What is the definition of a Hypermorph mutation?

Answer 324

Gain-of-function ## Footnote Produces too much of the normal protein or makes the protein overactive.

Question 325

What is the effect of a Hypermorph mutation?

Answer 325

Produces too much of the normal protein or makes the protein overactive ## Footnote This can lead to increased activity of the gene product.

Question 326

What are the common causes of a Hypermorph mutation?

Answer 326

* Enhanced transcription * Stabilization or activation of protein ## Footnote These factors contribute to the gain of function.

Question 327

What is the dominance pattern of a Hypermorph mutation?

Answer 327

Usually dominant ## Footnote This indicates that the mutant phenotype is expressed over the wild-type.

Question 328

What is the definition of a Neomorph mutation?

Answer 328

Gain-of-function, but with a new or different function ## Footnote The protein gains a novel activity not present in the wild-type.

Question 329

What is an example of a Neomorph mutation?

Answer 329

Binds a new substrate, functions in a different tissue, or activates in a new time window ## Footnote This illustrates the novel activities conferred by Neomorph mutations.

Question 330

What is the dominance pattern of a Neomorph mutation?

Answer 330

Usually dominant ## Footnote This means the new function is expressed over the wild-type function.

Question 331

What is the definition of an Antimorph (Dominant Negative) mutation?

Answer 331

A dominant negative mutation ## Footnote The mutant protein blocks the function of the wild-type protein.

Question 332

What is the effect of an Antimorph mutation?

Answer 332

The mutant protein blocks the function of the wild-type protein ## Footnote Often occurs when proteins function as dimers or complexes.

Question 333

What is a common example of an Antimorph mutation?

Answer 333

One mutant copy poisons the entire protein complex ## Footnote This demonstrates the dominant negative effect on protein function.

Question 334

What is the dominance pattern of an Antimorph mutation?

Answer 334

Dominant ## Footnote This is opposite in function to the wild-type.

Question 335

How do geneticists identify mutation types?

Answer 335

By observing how they behave when: * Homozygous * Heterozygous with deletion, wild-type, or duplication alleles ## Footnote This helps in classifying mutations based on their effects.

Question 336

What is an amorph mutation?

Answer 336

A complete loss-of-function mutation that produces no active product (null).

Question 337

What is a hypomorph mutation?

Answer 337

A partial loss-of-function mutation that makes a weak or leaky protein.

Question 338

What do amorphs and hypomorphs have in common?

Answer 338

Both are usually recessive to wild-type due to haplo-sufficiency.

Question 339

What is a hypermorph mutation?

Answer 339

A gain-of-function mutation that increases the normal activity or amount of protein.

Question 340

What is a neomorph mutation?

Answer 340

A gain-of-function mutation where the protein acquires a new or abnormal function.

Question 341

What is an antimorph mutation?

Answer 341

A dominant negative mutation that interferes with the wild-type protein function.

Question 342

Why are antimorphs dominant?

Answer 342

Because they act against the normal function, often poisoning protein complexes.

Question 343

How do you identify a mutation type experimentally?

Answer 343

Cross the mutant with deletion, wild-type, and duplication alleles and observe the phenotype.

Question 344

What are the five Muller’s Morphs?

Answer 344

* Amorph * Hypomorph * Hypermorph * Neomorph * Antimorph

Question 345

What is a silent mutation?

Answer 345

A base substitution in DNA that does not affect the phenotype. ## Footnote The amino acid sequence of the protein may remain unchanged or the protein function is not affected.

Question 346

Why are silent mutations common?

Answer 346

They often do not cause visible phenotypic effects and are often single base substitutions. ## Footnote This is due to the location of mutation and the degeneracy of the genetic code.

Question 347

What types of regions can silent mutations occur in?

Answer 347

* Inter-genic regions (between genes) * Intron regions (within a gene but not translated) ## Footnote Mutations in these regions may not affect the final protein product.

Question 348

What is the degeneracy of the genetic code?

Answer 348

The genetic code is redundant, meaning multiple codons code for the same amino acid. ## Footnote Example: GCT, GCC, GCA, and GCG all code for alanine.

Question 349

What happens if a base change occurs within a codon?

Answer 349

It might still specify the same amino acid. ## Footnote This can lead to a silent mutation where the protein function is unaffected.

Question 350

What are functionally tolerant substitutions?

Answer 350

Amino acid changes that do not alter the protein’s function. ## Footnote These changes are still considered silent in effect, as no phenotypic consequence is observed.

Question 351

What is the significance of silent mutations?

Answer 351

They are usually harmless and useful for studying mutation rates without causing functional damage. ## Footnote They often go undetected unless DNA is sequenced directly.

Question 352

True or False: Silent mutations can be detected without DNA sequencing.

Answer 352

False ## Footnote Silent mutations often go undetected unless DNA is sequenced directly.

Question 353

Fill in the blank: Silent mutations are often _______ base substitutions.

Answer 353

single ## Footnote This characteristic contributes to their commonality.

Question 354

What is a silent mutation?

Answer 354

A base change that does not affect the organism's phenotype. ## Footnote Silent mutations can occur in coding or non-coding regions.

Question 355

Why are silent mutations common after mutagen treatment?

Answer 355

Because many changes occur in non-coding regions or don’t affect the protein product. ## Footnote Mutagens can induce various types of mutations, many of which are silent.

Question 356

What are inter-genic regions?

Answer 356

Non-coding DNA regions located between genes. ## Footnote These regions can contain regulatory elements and are important for gene expression.

Question 357

Can a base change in a coding region still be silent?

Answer 357

Yes, if the new codon codes for the same amino acid (due to genetic code degeneracy). ## Footnote Codons can vary while still coding for the same amino acid.

Question 358

What is genetic code degeneracy?

Answer 358

The fact that multiple codons can specify the same amino acid. ## Footnote This property of the genetic code provides a buffer against mutations.

Question 359

Give an example of codons that all code for the same amino acid.

Answer 359

GCT, GCC, GCA, and GCG all code for alanine. ## Footnote These are examples of synonymous codons for the amino acid alanine.

Question 360

Can an amino acid change still result in a silent effect?

Answer 360

Yes, if the change doesn’t alter the protein’s function. ## Footnote Functional redundancy in proteins can allow for some variations without affecting overall activity.

Question 361

Why might silent mutations not affect phenotype?

Answer 361

Because either the protein isn’t altered or the altered amino acid doesn’t affect function. ## Footnote Silent mutations can contribute to genetic variation without phenotypic consequences.

Question 362

What is one reason mutations may not produce observable phenotypes?

Answer 362

Environmental Influence ## Footnote A gene's role might be essential in one condition but irrelevant in another, affecting phenotype expression.

Question 363

How can environmental conditions affect phenotypes related to mutations?

Answer 363

A homozygous loss-of-function mutation might not show any phenotype under standard lab conditions but would show one in a different environment.

Question 364

What is genetic redundancy?

Answer 364

Some genes in the genome perform overlapping or similar functions.

Question 365

What happens if one gene is lost or mutated in the context of genetic redundancy?

Answer 365

Another gene compensates, so no phenotype appears, even though the gene is nonfunctional.

Question 366

What are paralogs?

Answer 366

Evolutionarily related and functionally similar genes.

Question 367

Why might mutant screens miss important genes?

Answer 367

Because no phenotype emerges when only one gene is mutated due to redundancy.

Question 368

What are the limitations of mutant screening?

Answer 368

* It may not detect genes with redundant functions. * It may miss environment-specific phenotypes.

Question 369

What is crucial for accurate gene function discovery?

Answer 369

Combining genetic screening with molecular tools and different conditions.

Question 370

Fill in the blank: The effect of a mutation may depend on the _______.

Answer 370

[environment]

Question 371

True or False: Mutations always produce observable phenotypes.

Answer 371

False

Question 372

Why is the developmental stage important in observing traits?

Answer 372

Some traits can only be observed if the organism survives to a certain developmental stage, such as flower color in mature plants and eye color in flies after eye development. ## Footnote Traits that are not visible until a specific stage can lead to misleading conclusions if the organism does not reach that stage due to mutations.

Question 373

What are essential genes?

Answer 373

Essential genes are genes required for survival or proper development. ## Footnote Mutations in essential genes can lead to the death of the organism before phenotypic analysis can occur.

Question 374

What is a recessive lethal allele?

Answer 374

A mutation in an essential gene that causes homozygous individuals to die, often during the embryonic stage. ## Footnote These individuals will not be present among the surviving progeny, leading to gaps in phenotypic data.

Question 375

How do lethal alleles affect genetic screens?

Answer 375

Lethal alleles can go undetected in normal mutant screens because dead embryos do not develop enough to be scored. ## Footnote This can distort expected phenotypic ratios in a monohybrid cross, such as a 1:0 ratio instead of the expected 3:1.

Question 376

What phenotypic ratio distortion can occur due to recessive lethal alleles?

Answer 376

1:0 ratio, where all progeny show the same phenotype because the part that would show the mutation is missing due to death. ## Footnote This can mislead researchers about the inheritance patterns of traits.

Question 377

Fill in the blank: Mutations in essential genes can ______ detection.

Answer 377

escape ## Footnote Phenotypic screening only captures what survives, making lethal mutations invisible unless specifically tested.

Question 378

True or False: All traits can be observed regardless of the developmental stage of the organism.

Answer 378

False ## Footnote Some traits require the organism to reach a specific developmental stage to be visible.

Question 379

What are essential genes?

Answer 379

Genes required for survival or normal development of an organism. ## Footnote Essential genes are critical for the organism's life cycle and functioning.

Question 380

What is a recessive lethal allele?

Answer 380

A mutated allele that causes death when present in two copies (homozygous). ## Footnote This type of allele can significantly impact genetic studies and inheritance patterns.

Question 381

Why might a mutation in an essential gene go unnoticed?

Answer 381

Because homozygous mutants die early and never reach the stage where phenotype can be observed. ## Footnote This phenomenon complicates the analysis of genetic traits.

Question 382

Why can’t some phenotypes be scored in young organisms?

Answer 382

Because the trait requires a specific developmental stage (e.g., flower color, eye color). ## Footnote Certain traits manifest only after certain growth milestones.

Question 383

What is the phenotypic ratio in a monohybrid cross with a recessive lethal allele?

Answer 383

1:0 (all surviving offspring show the same phenotype; lethals are missing). ## Footnote This ratio indicates that no individuals with the lethal phenotype are present.

Question 384

Why is the 1:0 ratio equivalent to 3:0 in this context?

Answer 384

Because the expected 1 part with the mutant phenotype is missing due to death, so only the 3 wild-type-like individuals survive. ## Footnote This illustrates how lethal alleles affect expected genetic ratios.

Question 385

How do recessive lethal alleles limit mutant screening?

Answer 385

They remove affected individuals from the population before scoring is possible. ## Footnote This creates challenges in identifying and studying certain genetic traits.

Question 386

How are genes typically named?

Answer 386

Based on what goes wrong when the gene is mutated, not its normal function ## Footnote This leads to names that can be misleading, as they do not reflect the gene's wild-type function.

Question 387

What is the mutant phenotype of the 'white' gene in Drosophila?

Answer 387

White eyes ## Footnote The wild-type allele of the 'white' gene causes red eyes.

Question 388

What is the wild-type phenotype of the 'white' gene in Drosophila?

Answer 388

Red eyes ## Footnote This is the normal phenotype when the gene is not mutated.

Question 389

Why can't the 'white' gene be named 'red'?

Answer 389

More than a dozen genes contribute to red eye pigment in flies ## Footnote These include genes like violet, cinnabar, brown, and scarlet.

Question 390

What issue arises with naming lethal mutants?

Answer 390

They are often named for the way the organism dies, which can be vague or misleading ## Footnote Examples include even-skipped, hunchback, hairy, and runt.

Question 391

What strategies do scientists use to reduce naming confusion of genes?

Answer 391

Assign gene numbers, chromosomal locations, or descriptive names based on: * Developmental roles * How the organism dies * Physical appearance of the mutant ## Footnote These strategies help clarify gene functions and characteristics.

Question 392

How are many genes named in genetics?

Answer 392

After their mutant phenotype, not their normal function.

Question 393

Why is the 'white' gene in Drosophila misleading?

Answer 393

Because its wild-type function gives red eyes, but it’s named after the mutant white eye phenotype.

Question 394

What does the white gene do in wild-type fruit flies?

Answer 394

It imports pigment precursors to produce red eye color.

Question 395

Why don’t we call the white gene 'red'?

Answer 395

Because many genes affect red eye color—naming them all 'red' would be confusing.

Question 396

Name three genes involved in Drosophila eye color other than white.

Answer 396

* cinnabar * brown * violet * scarlet

Question 397

What problem arises when naming lethal mutations?

Answer 397

The gene is named based on how the mutant dies, which can be vague or non-informative.

Question 398

Give examples of descriptive gene names based on lethal phenotype.

Answer 398

* even-skipped * hunchback * hairy * runt

Question 399

How do scientists avoid naming confusion?

Answer 399

By using gene numbers, chromosomal positions, or descriptive mutant-based names.

Question 400

Why do we use complementation tests?

Answer 400

To determine if two different mutations affect the same gene or different genes in the same pathway ## Footnote This is important because multiple genes can produce the same observable trait.

Question 401

What is the difference between allelic and non-allelic mutations?

Answer 401

Allelic mutations occur in the same gene, while non-allelic mutations occur in different genes affecting the same phenotype.

Question 402

What is a complementation test?

Answer 402

An experimental method to combine two mutants with the same phenotype to see if they restore the wild-type phenotype in offspring.

Question 403

How does a complementation test work?

Answer 403

Cross two mutant organisms and observe the offspring's phenotype to determine if complementation occurred.

Question 404

What indicates that mutations are in different genes during a complementation test?

Answer 404

If the offspring show a normal phenotype, indicating complementation occurred.

Question 405

What indicates that mutations are in the same gene during a complementation test?

Answer 405

If the offspring still show the mutant phenotype, indicating no complementation.

Question 406

Fill in the blank: Complementation indicates mutations are in _______ genes.

Answer 406

different

Question 407

Fill in the blank: No complementation indicates mutations are in the _______ gene.

Answer 407

same

Question 408

What does complementation help clarify?

Answer 408

How many genes are involved in producing a phenotype.

Question 409

What is required for purple pigment production in flowers?

Answer 409

Two genes working in sequence ## Footnote Gene A and Gene B are essential for the conversion of compounds leading to purple pigment.

Question 410

What does Gene A encode?

Answer 410

Enzyme #1, converting compound #1 → compound #2 ## Footnote This is the first step in the biochemical pathway for purple pigment production.

Question 411

What does Gene B encode?

Answer 411

Enzyme #2, converting compound #2 → purple pigment ## Footnote This is the final step in the biochemical pathway for producing purple pigment.

Question 412

What is the phenotype of AABB?

Answer 412

Wild-type = purple ## Footnote AABB represents the genotype that leads to the production of purple pigment.

Question 413

What is the phenotype of aaBB?

Answer 413

White (can't convert #1 to #2) ## Footnote This indicates a mutation in Gene A that prevents pigment production.

Question 414

What is the phenotype of AAbb?

Answer 414

White (can’t convert #2 to pigment) ## Footnote This indicates a mutation in Gene B.

Question 415

What is the result if either enzyme is non-functional in aaBb or AaBB?

Answer 415

Still white ## Footnote The flower remains white if either gene is mutated.

Question 416

What is the genotype of the offspring when crossing aaBB and AAbb?

Answer 416

AaBb ## Footnote This represents the combination of alleles from both parents.

Question 417

What does the AaBb offspring phenotype indicate?

Answer 417

Purple flower (wild-type phenotype) ## Footnote The presence of one working allele from each parent allows for enzyme production.

Question 418

What does complementation show?

Answer 418

The mutations are in different genes ## Footnote This is a key aspect of how complementation tests determine genetic interactions.

Question 419

What happens when two white-flowered plants have mutations in the same gene?

Answer 419

Offspring are still white (aaBB) ## Footnote This indicates that the mutations are allelic and do not complement each other.

Question 420

What do complementation tests determine?

Answer 420

Whether similar phenotypes result from mutations in the same gene (allelic) or different genes (non-allelic) ## Footnote This is crucial for understanding genetic interactions and pathways.

Question 421

Fill in the blank: Complementation restores the phenotype only when each parent contributes the gene the other _______.

Answer 421

lacks ## Footnote This is the fundamental principle behind complementation in genetics.

Question 422

What question does a complementation test help answer?

Answer 422

Whether two similar mutant phenotypes are due to mutations in the same gene or different genes.

Question 423

What are allelic mutations?

Answer 423

Mutations in the same gene.

Question 424

What are non-allelic mutations?

Answer 424

Mutations in different genes.

Question 425

What is a complementation test?

Answer 425

A test that crosses two mutants to see if their offspring recover the wild-type phenotype.

Question 426

What does it mean if two mutations complement each other?

Answer 426

They are in different genes (non-allelic).

Question 427

What does it mean if two mutations do not complement?

Answer 427

They are in the same gene (allelic).

Question 428

What phenotype do offspring show if mutations are in the same gene?

Answer 428

The mutant phenotype (no complementation).

Question 429

What phenotype do offspring show if mutations are in different genes?

Answer 429

The wild-type phenotype (complementation occurred).

Question 430

What is required for purple pigment production in flowers?

Answer 430

Two genes working in sequence ## Footnote Gene A and Gene B are essential for the conversion of compounds leading to purple pigment.

Question 431

What does Gene A encode?

Answer 431

Enzyme #1, converting compound #1 → compound #2 ## Footnote This is the first step in the biochemical pathway for purple pigment production.

Question 432

What does Gene B encode?

Answer 432

Enzyme #2, converting compound #2 → purple pigment ## Footnote This is the final step in the biochemical pathway for producing purple pigment.

Question 433

What is the phenotype of AABB?

Answer 433

Wild-type = purple ## Footnote AABB represents the genotype that leads to the production of purple pigment.

Question 434

What is the phenotype of aaBB?

Answer 434

White (can't convert #1 to #2) ## Footnote This indicates a mutation in Gene A that prevents pigment production.

Question 435

What is the phenotype of AAbb?

Answer 435

White (can’t convert #2 to pigment) ## Footnote This indicates a mutation in Gene B.

Question 436

What is the result if either enzyme is non-functional in aaBb or AaBB?

Answer 436

Still white ## Footnote The flower remains white if either gene is mutated.

Question 437

What is the genotype of the offspring when crossing aaBB and AAbb?

Answer 437

AaBb ## Footnote This represents the combination of alleles from both parents.

Question 438

What does the AaBb offspring phenotype indicate?

Answer 438

Purple flower (wild-type phenotype) ## Footnote The presence of one working allele from each parent allows for enzyme production.

Question 439

What does complementation show?

Answer 439

The mutations are in different genes ## Footnote This is a key aspect of how complementation tests determine genetic interactions.

Question 440

What happens when two white-flowered plants have mutations in the same gene?

Answer 440

Offspring are still white (aaBB) ## Footnote This indicates that the mutations are allelic and do not complement each other.

Question 441

What do complementation tests determine?

Answer 441

Whether similar phenotypes result from mutations in the same gene (allelic) or different genes (non-allelic) ## Footnote This is crucial for understanding genetic interactions and pathways.

Question 442

Fill in the blank: Complementation restores the phenotype only when each parent contributes the gene the other _______.

Answer 442

lacks ## Footnote This is the fundamental principle behind complementation in genetics.

Question 443

What does a complementation test assess?

Answer 443

Whether two mutants with the same phenotype have mutations in the same or different genes.

Question 444

In the purple flower example, what is the role of gene A?

Answer 444

It converts compound #1 into compound #2.

Question 445

What is the role of gene B in the purple pigment pathway?

Answer 445

It converts compound #2 into the final purple pigment.

Question 446

What is the phenotype of aaBB?

Answer 446

White flower (mutation in gene A).

Question 447

What is the phenotype of AAbb?

Answer 447

White flower (mutation in gene B).

Question 448

What is the phenotype of AaBb (offspring of aaBB × AAbb)?

Answer 448

Purple flower (wild-type) — complementation occurred.

Question 449

What does it mean if offspring from two mutants are still mutant?

Answer 449

The mutations are in the same gene (allelic) — no complementation.

Question 450

What does it mean if offspring of two mutants show the wild-type phenotype?

Answer 450

The mutations are in different genes (non-allelic) — complementation occurred.

Question 451

What are non-allelic mutations?

Answer 451

Mutations in different genes that affect the same pathway or trait.

Question 452

What are allelic mutations?

Answer 452

Mutations in the same gene, even if in different locations or forms.

Question 453

What is the purpose of a complementation test?

Answer 453

To determine if mutations are in the same gene or different genes.

Question 454

What is the first step in performing a complementation test?

Answer 454

Cross the two pure-breeding homozygous mutants.

Question 455

What should be observed in the F1 phenotype if no complementation occurs?

Answer 455

All F1 progeny have the mutant phenotype.

Question 456

What does it imply if no complementation is observed?

Answer 456

The parents must have had mutations in the same gene.

Question 457

What is the F1 genotype when no complementation occurs?

Answer 457

aaBB or AAbb.

Question 458

What is concluded when mutations are allelic?

Answer 458

No complementation occurred.

Question 459

What is observed in the F1 phenotype if complementation occurs?

Answer 459

All F1 progeny show the wild-type phenotype.

Question 460

What does it imply if complementation occurs?

Answer 460

The parents had mutations in different genes.

Question 461

What is the F1 genotype when complementation occurs?

Answer 461

AaBb.

Question 462

What is concluded when mutations are non-allelic?

Answer 462

Complementation occurred.

Question 463

What is restored when complementation occurs?

Answer 463

Function to the biochemical pathway.

Question 464

What is the first key condition for a valid complementation test?

Answer 464

Mutants must be homozygous at the mutant locus.

Question 465

What is the second key condition for a valid complementation test?

Answer 465

Mutations must be recessive.

Question 466

What can mask complementation?

Answer 466

Dominant mutations.

Question 467

What should be ensured about gene locus in each strain for a valid complementation test?

Answer 467

Only one gene locus should be mutated in each strain.

Question 468

What can confuse the results of a complementation test?

Answer 468

Multiple mutations.

Question 469

What is the goal of a complementation test?

Answer 469

To determine whether mutations with similar phenotypes are in the same gene or different genes.

Question 470

What does it mean if F1 progeny from two mutants are still mutant?

Answer 470

The mutations are allelic (in the same gene); no complementation occurred.

Question 471

What does it mean if F1 progeny are wild-type after a mutant cross?

Answer 471

The mutations are non-allelic (in different genes); complementation occurred.

Question 472

What kind of mutations cannot be used in complementation tests?

Answer 472

Dominant mutations, because they override the presence of wild-type alleles.

Question 473

What genotypes might cause a no-complementation result?

Answer 473

Either aaBB crossed with aaBB, or AAbb crossed with AAbb—mutations in the same gene.

Question 474

What is the genotype of a successful complementation result in the F1?

Answer 474

AaBb—heterozygous at both loci, with one wild-type allele at each.

Question 475

Why must the parent strains be pure-breeding for complementation testing?

Answer 475

To ensure both carry homozygous mutations that can be unambiguously tested in F1.

Question 476

Can multiple mutations in one strain affect a complementation test?

Answer 476

Yes, it may fail to complement even if the two strains’ main mutations are in different genes.

Question 477

What is Cystic Fibrosis?

Answer 477

CF is the most common life-limiting autosomal recessive disease in people of European descent. ## Footnote Frequency: 1 in 2,500 live births, with about 1 in 25 people being carriers.

Question 478

What gene mutation causes Cystic Fibrosis?

Answer 478

Mutations in the CFTR gene (Cystic Fibrosis Transmembrane Conductance Regulator) cause CF. ## Footnote CFTR is responsible for encoding a chloride ion channel.

Question 479

What role does CFTR play in normal cells?

Answer 479

CFTR encodes a chloride ion channel found in epithelial cells. ## Footnote It regulates liquid layer thickness on epithelial surfaces and is necessary for mucus clearance.

Question 480

What is the consequence of CFTR mutations?

Answer 480

Mutations lead to impaired ion transport and mucus buildup. ## Footnote This results in increased infections, lung damage, and problems in multiple organs.

Question 481

What is the most common mutation associated with Cystic Fibrosis?

Answer 481

The most common mutation is ΔF508 / PHE508DEL. ## Footnote It involves a deletion of three nucleotides, leading to loss of phenylalanine at position 508.

Question 482

What does the ΔF508 mutation prevent?

Answer 482

It prevents proper folding of the CFTR protein in the endoplasmic reticulum. ## Footnote Misfolded CFTR is destroyed before reaching the cell membrane.

Question 483

What percentage of CF cases in North America does the ΔF508 mutation account for?

Answer 483

About 70% of CF cases in North America. ## Footnote There is speculation that carriers may have had evolutionary advantages.

Question 484

Which drug was approved for CF treatment in 2012?

Answer 484

Kalydeco was approved by FDA and Health Canada in 2012. ## Footnote It works on specific mutations like G551D.

Question 485

What mutation does Kalydeco target?

Answer 485

Kalydeco targets the G551D mutation. ## Footnote G551D is a substitution of glycine for aspartic acid at position 551.

Question 486

What is the cost of Kalydeco per year per patient?

Answer 486

The cost is approximately $250,000 per year per patient.

Question 487

Is Cystic Fibrosis a monogenic disorder?

Answer 487

Yes, CF is a monogenic, autosomal recessive disorder. ## Footnote It has a clear molecular basis linked to the CFTR gene.

Question 488

Fill in the blank: The channel that CFTR encodes opens in response to _______.

Answer 488

ATP

Question 489

True or False: The CFTR channel functions properly in all CF patients.

Answer 489

False

Question 490

What gene is mutated in cystic fibrosis?

Answer 490

CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) ## Footnote The CFTR gene is crucial for the proper functioning of epithelial tissues.

Question 491

What is the inheritance pattern of CF?

Answer 491

Autosomal recessive ## Footnote This means that an individual must inherit two copies of the mutated gene to express the condition.

Question 492

What is the role of the CFTR protein?

Answer 492

It is a chloride ion channel that regulates ion and water movement in epithelial tissues. ## Footnote Proper CFTR function is essential for maintaining fluid balance in various organs.

Question 493

What is the most common CF-causing mutation?

Answer 493

ΔF508 / PHE508DEL — deletion of phenylalanine at position 508. ## Footnote This mutation is responsible for a significant percentage of cystic fibrosis cases.

Question 494

How does the ΔF508 mutation affect CFTR?

Answer 494

It causes misfolding, leading to degradation in the ER and absence at the membrane. ## Footnote This prevents the CFTR protein from reaching the cell surface where it functions.

Question 495

What are some organs affected by CF?

Answer 495

Lungs, pancreas, liver, intestines, sweat glands, and reproductive organs. ## Footnote Cystic fibrosis can lead to severe complications in these organs due to thickened secretions.

Question 496

What is the genotype of a carrier of CF?

Answer 496

Heterozygous for a CFTR mutation. ## Footnote Carriers do not show symptoms but can pass the mutation to their offspring.

Question 497

What does the G551D mutation affect?

Answer 497

ATP binding, preventing channel opening. ## Footnote This mutation alters the CFTR protein's ability to function properly.

Question 498

What drug treats some CFTR mutations by keeping the channel open?

Answer 498

Kalydeco ## Footnote Kalydeco is a CFTR modulator that improves function in specific mutations.

Question 499

How much does Kalydeco cost per patient per year?

Answer 499

Around $250,000 ## Footnote The high cost of treatment can be a barrier for many patients.

Question 500

Why might ΔF508 carriers have had an evolutionary advantage?

Answer 500

They may have had reduced water loss. ## Footnote This could have provided a selective advantage in certain environments, such as those with high prevalence of cholera.

Question 501

What are the similarities between polymorphisms and mutations?

Answer 501

Both are changes in the DNA sequence

Question 502

What is the key difference between polymorphisms and mutations?

Answer 502

Frequency and impact: polymorphisms are common (>1% of individuals), mutations are rare

Question 503

What are some observable effects of polymorphisms?

Answer 503

May have no observable effect or result in normal variation like differences in eye color or blood types

Question 504

What are mutations often associated with?

Answer 504

Disease or altered function

Question 505

What types of mutations can substitutions result in?

Answer 505

* Silent * Missense * Nonsense

Question 506

What are some causes of substitution mutations?

Answer 506

* Tautomeric shifts * Alkylating agents * Irradiation * Spontaneous replication errors

Question 507

What is a deletion in a DNA sequence?

Answer 507

The loss of one or more nucleotides

Question 508

What can cause deletions in a DNA sequence?

Answer 508

* Strand slippage during DNA replication * Radiation breaking DNA strands * Chemical mutagens * Errors during recombination

Question 509

What is an insertion in a DNA sequence?

Answer 509

The addition of extra nucleotide bases

Question 510

What are some causes of insertions in a DNA sequence?

Answer 510

* Strand slippage * Transposons * DNA polymerase errors * Chromosomal duplications

Question 511

What health hazards are associated with smoking tobacco?

Answer 511

Contains benzopyrene, a potent mutagen linked to lung cancer

Question 512

What is the effect of benzopyrene on DNA?

Answer 512

* Intercalating agent * Causes distortion of the double helix * Leads to point mutations and deletions

Question 513

What hypothesis explains the skewed sex ratio in fruit fly mutagenesis?

Answer 513

A recessive, X-linked lethal mutation causes a 2:1 female-to-male ratio

Question 514

How can the hypothesis about sex ratio be tested?

Answer 514

Perform a reciprocal cross and observe the survival of male offspring

Question 515

What is the first step in screening for genes required for floral scent?

Answer 515

Mutagenize seeds (e.g., EMS treatment)

Question 516

What does the 'fishy' mutant suggest?

Answer 516

A gene converts a smelly intermediate into a pleasant-scented final product

Question 517

What does the 'nosmell' mutant suggest?

Answer 517

* Affects a gene upstream of fishy * May impact a transporter or enzyme essential for scent function

Question 518

What is the expected frequency of dominant mutations?

Answer 518

Rarer than recessive mutations due to the requirement for gain-of-function

Question 519

How can dominant mutations be screened?

Answer 519

Focus on the F₁ generation; any F₁ plant showing the trait suggests dominance

Question 520

What type of mutagen is best for creating dominant mutations?

Answer 520

Point mutagens (e.g., EMS) are more likely to create dominant mutations

Question 521

Which transposons are transcribed?

Answer 521

Class I transposons (retrotransposons) are transcribed into RNA

Question 522

What is the screening plan for proline synthesis genes?

Answer 522

Mutagenize auxotrophic strain and select Pro⁻ mutants

Question 523

How can different genes be distinguished in proline synthesis mutants?

Answer 523

* Mapping * Response to precursors * Complementation tests

Question 524

What is the F₁ phenotype if mutants are in different genes?

Answer 524

Wild-type; F₁ would grow without proline

Question 525

What is the F₁ phenotype if mutants are in the same gene?

Answer 525

Mutant; F₁ would fail to grow without proline