Chapter 14: Gene Mutation, Repair, and Transposition

Question 1

True or False. A mutation can be defined as an alteration in DNA sequence. Any base-pair change in any part of a DNA molecule can be considered a mutation.

Answer 1

True

Question 2

True or False. Mutations that occur in somatic cells are heritable and are the basis for the transmission of genetic diversity and evolution, as well as genetic diseases.

Answer 2

False. Germ cells

Question 3

The type of mutation that involves a change of one base pair to another in a DNA molecule.

Answer 3

Point mutation or Base substitution

Question 4

A change of one nucleotide of a triplet within a protein-coding portion of a gene may result in the creation of a new triplet that codes for a different amino acid in the protein product. This type of mutation is called?

Answer 4

Missense mutation

Question 5

A change of one nucleotide of a triplet within a protein-coding portion of a gene may result in the creation of a stop codon. This mutation is called?

Answer 5

Nonsense mutation

Question 6

If the point mutation alters a codon but does not result in a change in the amino acid at that position in the protein (due to degeneracy of the genetic code), this mutation is called?

Answer 6

Silent mutation

Question 7

In a base substitution mutation, a pyrimidine replaces a pyrimidine or a purine replaces a purine. This mutation is referred to as?

Answer 7

Transition mutation

Question 8

In a base substitution mutation, a purine replaces a pyrimidine or vice versa. This mutation is referred to as?

Answer 8

Transversion mutation

Question 9

A mutation, either an insertion or deletion of nucleotides, that alters the triplet reading frame is called?

Answer 9

Frameshift mutation

Question 10

True or False. A frameshift mutation will occur when any number of bases are added or deleted, except multiples of three, which would reestablish the initial frame of reading.

Answer 10

True

Question 11

A type of mutation that reduces or eliminates the function of the gene product.

Answer 11

Loss-of-function mutation

Question 12

Mutations that result in complete loss of function are known as?

Answer 12

Null mutations

Question 13

True or False. Most loss-of-function mutations are dominant.

Answer 13

False. Recessive

Question 14

Results in a wild-type phenotype when present in a diploid organism and the other allele is wild type.

Answer 14

Recessive mutation

Question 15

Results in a mutant phenotype in a diploid organism, even when the wild-type allele is also present.

Answer 15

Dominant mutation

Question 16

Occurs when the single wild-type copy of the gene does not produce enough gene product to bring about a wild-type phenotype.

Answer 16

Haploinssufficiency

Question 17

This disease in humans is an example of a disorder caused by haploinsufficiency—in this case as a result of a loss-of-function mutation in one copy of the FBN1 gene.

Answer 17

Marfan syndrome

Question 18

This mutation results in a gene product with enhanced, negative, or new functions.

Answer 18

Dominant gain-of-function mutation

Question 19

Causes of dominant gain-of-function mutation.

Answer 19

1. Change in the amino acid sequence of the protein that confers a new activity
2. A mutation in a regulatory region of the gene, leading to expression of the gene at higher levels or at abnormal times or places.

Question 20

This type of mutation may directly interfere with the function of the product of the wild-type allele. Often this occurs when the mutant nonfunctional gene product binds to the wild-type gene product, inactivating it.

Answer 20

Dominant negative mutation

Question 21

These mutations are recognized by their ability to alter a normal or wild-type visible phenotype.

Answer 21

Visible mutation

Question 22

This mutation results in a loss of ability to synthesize an amino acid or vitamin.

Answer 22

Nutritional mutation

Question 23

Although these kinds of mutations do not always affect morphological characters, they affect the function of proteins that can impinge on the well-being and survival of the affected individual.

Answer 23

Biochemical mutation

Question 24

This category of mutations consists of mutations that affect the behavior patterns of an organism.

Answer 24

Behavioral mutations

Question 25

This kind of mutation disrupts a regulatory gene or a gene control region which results in the disruption of the normal regulatory processes and inappropriate activation or inactivation of a gene.

Answer 25

Regulator mutations

Question 26

This kind of mutation adversely affects a gene product that is essential to the survival of the organism.

Answer 26

Lethal mutation

Question 27

These mutations are present in the genome of an organism but can be detected only under certain conditions.

Answer 27

Conditional mutations

Question 28

This is a type of conditional mutation whereby at a “permissive” temperature, the mutant gene product functions normally, but it loses its function at a different, “restrictive” temperature.

Answer 28

Temperature-senstive mutations

Question 29

A mutation that can occur either in a protein-coding region or in any part of the genome, and its effect on the genetic fitness of the organism is negligible.

Answer 29

Neutral mutation

Question 30

Mutations that are occurring in any cell in the body except germ cells.

Answer 30

Somatic mutations

Question 31

Are mutations within genes located on the autosomes.

Answer 31

Autosomal mutations

Question 32

Are mutations within genes located on the X chromosome.

Answer 32

X-linked mutation

Question 33

Are mutations within genes located on the Y chromosome.

Answer 33

Y-linked mutation

Question 34

True or False. Somatic mutations will have a greater impact if they are dominant or, in males, if they are X-linked since such mutations are most likely to be immediately expressed.

Answer 34

True

Question 35

Are mutations in the nucleotide sequence of genes that appear to occur naturally.

Answer 35

Spontaneous mutation

Question 36

Are mutations that result from the influence of extraneous factors.

Answer 36

Induced mutations

Question 37

Defined as the likelihood that a gene will undergo a mutation in a single generation or in forming a single gamete.

Answer 37

Mutation rate

Question 38

Some DNA sequences appear to be highly susceptible to mutation and are known as?

Answer 38

Mutation Hotspot

Question 39

Are alternate chemical forms that differ by only a single proton shift in the molecule.

Answer 39

Tautomers

Question 40

The biologically important tautomers:

Answer 40

1. keto-enol forms of thymine | 2. amino-imino forms of cytosine and adenine

Question 41

This shift changes the bonding structure of the molecule, allowing hydrogen bonding with noncomplementary bases.

Answer 41

Tautomeric shift

Question 42

The loss of one of the nitrogenous bases in an intact double-helical DNA molecule. Most frequently, the base is a purine—either guanine or adenine.

Answer 42

Depurination

Question 43

This results if the glycosidic bond linking the 1′-C of the deoxyribose and the number 9 position of the purine ring is broken.

Answer 43

Apurinic site

Question 44

An amino group in cytosine or adenine is converted to a keto group. The major effect of these changes is an alteration in the base-pairing specificities of these two bases during DNA replication.

Answer 44

Deamination

Question 45

DNA may also suffer damage from the by-products of normal cellular processes. These damages are often caused by reactive oxygen species (electrophilic oxidants) that are generated during normal aerobic respiration.

Answer 45

Oxidative damage

Question 46

Are mutations that increase the rate of mutation above the spontaneous background.

Answer 46

Induced mutations

Question 47

Agents that have the potential to damage DNA and cause induced mutations.

Answer 47

Mutagens

Question 48

Compounds that can substitute for purines or pyrimidines during nucleic acid biosynthesis.

Answer 48

Base Analogs

Question 49

A derivative of uracil, behaves as a thymine analog but is halogenated at the number 5 position of the pyrimidine ring.

Answer 49

5-bromouracil (5-BU)

Question 50

If 5-BU is chemically linked to deoxyribose, what nucleoside analog is formed?

Answer 50

bromodeoxyuridine (BrdU)

Question 51

This molecule can act as na analog of adenine.

Answer 51

2-amino purine (2-AP)

Question 52

These substances donate an alkyl group, such as CH3 or CH3CH2 to amino or keto groups in nucleotide.

Answer 52

Alkylating agents

Question 53

An alkylating agent that alkylates the keto groups in the number 6 position of guanine and in the number 4 position of thymine.

Answer 53

Ethylmethane sulfonate (EMS)

Question 54

Are chemicals that have dimensions and shapes that allow them to wedge between the base pairs of DNA.

Answer 54

Intercalating agents

Question 55

A substance that covalently binds to DNA, altering its conformation and interfering with replication and repair.

Answer 55

Adduct-forming agents

Question 56

Are cancer-causing chemicals that are created during the cooking of meats such as beef, chicken, and fish. They are formed at high temperatures from amino acids and creatine.

Answer 56

Heterocyclic amines (HCAs)

Question 57

Chemical species resulting from increased amount of UV introduced to the DNA and are consist of two thymine residues.

Answer 57

Pyrimidine dimers

Question 58

Radiation that causes ionization of the molecules.

Answer 58

Ionizing radiation

Question 59

These are chemical species containing one or more unpaired electrons.

Answer 59

Free-radicals

Question 60

These are genetic disease caused by variations in several genes.

Answer 60

Polygenic

Question 61

These are genetic disease caused by variations in single-gene mutations.

Answer 61

Monogenic

Question 62

During this repair mechanism, the mismatches are detected, the incorrect nucleotide is removed, and the correct nucleotide is inserted in its place.

Answer 62

Mismatch repair

Question 63

The process of strand discrimination is based on?

Answer 63

DNA methylation

Question 64

This enzyme methylates adenine upon its addition to the growing DNA sequence. Prior to methylation, however, it also detects base mismatches.

Answer 64

Adenine methylase

Question 65

This enzyme nicks the backbone of the unmethylated DNA (either in the 5' or 3' end of the mismatch) due to mismatching as detected by the adenine methylase.

Answer 65

Endonuclease

Question 66

This enzyme unwinds and degrades the nicked DNA strand until the region of the mismatch is reached.

Answer 66

exonuclease

Question 67

The human equivalent of MutH, MutL, and MutS genes. Associated with hereditary nonpolyposis colon cancer.

Answer 67

hMSH2, hMLH1 genes

Question 68

This repair mechanism responds after damaged DNA has escaped repair and has failed to be completely replicated.

Answer 68

postreplication repair

Question 69

Because the recombinational event is involved in postreplicational repair, it is considered to be?

Answer 69

homologous recombination repair.

Question 70

This protein directs the recombinational exchange with the corresponding region on the undamaged parental strand of the same polarity (the “donor” strand).

Answer 70

RecA

Question 71

In the presence of a large number of un-repaired DNA mismatches and gaps, bacteria can induce the expression of about 20 genes (including lexA, recA, and uvr) whose products allow DNA replication to occur even in the presence of these lesions. The repair mechanism is referred to as?

Answer 71

SOS repair system

Question 72

True or False. During SOS repair, DNA synthesis becomes error-prone, inserting random and possibly incorrect nucleotides in places that would normally stall DNA replication. As a result, SOS repair itself becomes mutagenic—although it may allow the cell to survive DNA damage that would otherwise kill it.

Answer 72

True

Question 73

UV-induced damage to E. coli DNA can be partially reversed if, following irradiation, the cells are exposed briefly to light in the blue range of the visible spectrum. This repair mechanism is called?

Answer 73

Photoreactivation repair

Question 74

Photoreactivation repair is directed by which enzyme?

Answer 74

photoreactivation enzyme (PRE)

Question 75

This type of excision repair mechanism corrects DNA that contains a damaged DNA base.

Answer 75

Base-excision repair

Question 76

The first step in the base excision repair pathway in E. coli involves the recognition of the altered base by an enzyme called?

Answer 76

DNA glycosylase

Question 77

In a base excision repair, the DNA glycosylase first cut the glycosidic bond between the base and the sugar, creating a?

Answer 77

apyrimidinic (if the base is pyrimidine) apurinic (if the base is purine) site

Question 78

In a base excision repair, the apurinic/apyrimidic site is recognized by?

Answer 78

AP endonuclease (makes a cut in the phosphodiester backbone at the apyrimidinic or apurinic site)

Question 79

This type of excision repair mechanism repair “bulky” lesions in DNA that alter or distort the double helix. These lesions include the UV-induced pyrimidine dimers and DNA adductss.

Answer 79

Nucleotide excision repair (NER)

Question 80

In the Nucleotide excision repair pathway products of this gene group are involved in recognizing and clipping out lesions in the DNA.

Answer 80

uvr (ultraviolet repair) genes - uvrA, uvrB, uvrC

Question 81

A rare recessive genetic disorder that predisposes individuals to severe skin abnormalities, skin cancers, and a wide range of other symptoms including developmental and neurological defects.

Answer 81

xeroderma pigmentosum (XP) (results from defects in NER pathways)

Question 82

XP patients were deficient in DNA synthesis other than that | occurring during chromosome replication. The later phenomenon is called?

Answer 82

unscheduled DNA synthesis

Question 83

It is a single cell with two nuclei from different organisms but a common cytoplasm.

Answer 83

Heterokaryon

Question 84

Are activated and are responsible for reattaching two broken DNA strands.

Answer 84

double-strand break repair (DSB repair) either (homologous recombination repair or nonhomologous end joining)

Question 85

A double-strand break repair mechanism that does not recruit a homologous region of DNA during repair.

Answer 85

nonhomologous end joining

Question 86

A double-strand break repair mechanism that involves the interaction of two sister chromatids is necessary because, when both strands of one helix are broken, there is no undamaged parental DNA strand available to use as a source of the complementary template DNA sequence during the repair.

Answer 86

homologous recombination repair

Question 87

True or False. DSB repair usually occurs during the late S or early G2 phase of the cell cycle, after DNA replication, a time when sister chromatids are available to be used as repair templates.

Answer 87

True

Question 88

This method uses a number of different strains of the bacterium Salmonella typhimurium that have been selected for their ability to reveal the presence of specific types of mutations.

Answer 88

Ames test

Question 89

Are cancer-causing agent

Answer 89

carcinogens

Question 90

Can move or transpose within and between chromosomes, inserting themselves into various locations within the genome.

Answer 90

Transposable elements or transposon or jumping genes

Question 91

This type of transposon can move from one location to | another and, if they insert into a gene or gene-regulatory region, may cause mutations.

Answer 91

Insertion sequences (IS elements)

Question 92

This enzyme, encoded by a gene present in insertion sequence elements, is responsible for making staggered cuts in chromosomal DNA, into which the IS element can insert.

Answer 92

Transposase

Question 93

These are short segments of DNA that have the same nucleotide sequence as each other but are oriented in the opposite direction. They are situated at the ends of IS elements.

Answer 93

inverted terminal repeats (ITRs)

Question 94

Are larger than IS elements and contain protein-coding genes that are unrelated to their transposition.

Answer 94

Bacterial transposons

Question 95

These elements are transcribed into "copious" amounts of RNA, hence the name.

Answer 95

copia

Question 96

A condition characterized by sterility, elevated mutation | rates, and chromosome rearrangements in the offspring of crosses between certain strains of fruit flies..

Answer 96

hybrid dygenesis

Question 97

Hybrid dysgenesis is caused by high rates of ______ transposition in the germ line, in which transposons insert themselves into or near genes, thereby causing mutations.

Answer 97

P element

Question 98

One of the most useful applications of P elements is as vectors to introduce transgenes into Drosophila—a technique known as ?

Answer 98

germ-line transformation