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BIO 226 > Final Review > Flashcards

Final Review Flashcards

Before Midterm

1
Q

Classical Genetics

A

Understanding the inheritance of phenotypes

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2
Q

Molecular genetics

A

Understanding the mechanisms of genetic regulation.

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3
Q

Assumed blending inheritance

A

average of parental phenotypes.

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4
Q

Most of our understanding came from plant/animal breeding

A

artificial selection

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5
Q

Gene

A

DNA sequence for a specific protein.
Generally, a specific region of the genome that codes for a particular protein; a specific locus.

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6
Q

Allele

A

A specific sequence of a gene, generally to compare between alleles of a single gene

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7
Q

Homozygote

A

In diploids, where both copies of a gene are the same allele-a genotype

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8
Q

Heterozygote

A

In diploids, where both copies of a gene are different alleles- a genotype

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9
Q

Dominant

A

Allele’s phenotype appears in both homozygotes and heterozygotes
Capital letters

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10
Q

Recessive

A

Allele’s phenotype only evident in homozygotes.
Lower case letters

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11
Q

Genotype

A

The genetic sequence of interest

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12
Q

Phenotype

A

The physical/cellular/protein results of a genotype and environmental effects.
Characteristics produced by different genotypes, also a response to the environment.

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13
Q

Features of the phenotype

A

dominant
recessive

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14
Q

If you cross 2 homozygotes with different alleles you will get

A

a heterozygote

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15
Q

P/P0

A

Parental cross (homozygote)
‘true breeding’

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16
Q

F1

A

First generation offspring/hybrid (heterozygotes).
Shows dominant phenotype, genotypes hidden.

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17
Q

F2

A

Second generation offspring/hybrids (not all heterozygotes).
Shows all possible phenotypes, can infer all genotypes.

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18
Q

Monohybrid cross

A

Looking at a single trait/gene.
Crosses of two varieties of true-breeding plants that differed in one character.

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19
Q

Dihybrid cross

A

Looking at 2 traits/genes
Crosses of two varieties of true-breeding plants that differed in two characters.
For every chracter, one trait is dominant and one trait is recessive.

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20
Q

Test cross

A

Determining unknown genotype by crossing an unknown individual with a homozygous recessive

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21
Q

Mendel’s peas

A

High number of progeny, easy to grow, short life cycle, easy to control mating (pollination)
Different varieties were readily available.
Two easily distinguishable states (tall or short)
No linkage
Traits controlled by single genes.

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22
Q

The fate of mendel’s genes

A

Identification of the mutations/genes for 4/7 traits so far.

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23
Q

Mendel’s approach 1

A

Designed crosses carefully and kept detailed records of each.
Counted the number of offspring that had the traits he was following.
Kept track of generations and followed inheritance over several generations.
Asked very specific questions and made testable predictions from results.

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24
Q

Mendel’s approach II

A

Key to his success:
Mendel created tru breeding lineages; plants were crossed repeatedly until all offspring looked like parentals-homozygotes. Mostly done through selfing.
Followed a key rule of the scientific method: good controls

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25
Q

Selfing

A

easy to make true breeding lineages amimals are too much work.

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26
Q

Mendel’s Experiment #1

A

Monohybrid cross: crosses of two varieties of true-bredding plants that differed in only one character. Only 1 phenotype appears in the F1 (dominant, no info about genotype). F2 shows all possible phenotypes from combinations of genotypes. VAst majority of the peas were still round.
Wrinkled information was not lost.

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27
Q

Mendel’s Conclusions I

A

There is a difference between a trait (phenotype) and the information for the trait (genotype).
Round seeds is the dominant phenotype- genotype is homozygous dominant RR or heterozygous Rr.
Wrinkled seeds is recessive- genotype is homozygous recessive rr.

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28
Q

Gene notation for round peas

A

Homozygote- RR
Heterozygote- Dominant allele listed first Rr
Dominant- Capital letters RR
Recessive- small letters rr

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29
Q

Gene notation for vestigial winged flies

A

Homozygote- +/+ vg/vg
Heterozygote- dominant allele listed first +/vg
+ indicates wildtype, not dominance.
Most of the time wildtype will be dominant.

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30
Q

Mendel’s conclusions II- modern terminology

A

Alternative versions of genes (different alleles) account for variation in inherited chracteristics.
Diploid organisms inherit two alleles, one from each parent.
If two alleles are different, one may be dominant.
Each haploid gamete carries only one allele of a given trait because they segregate from one during meiosis.

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31
Q

The First Mendelian Law

A

Law of segregation

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32
Q

Law of segregation

A

Alleles of a gene separate independently (randomly) from each other during transmission from parent to offspring (=meiosis).
The dominant phenotype appears at 100% in the F1 (hybrid genotype).
The phenotypic frequencies in F2 conforms to: 3:1 (dominant:recessive)

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33
Q

How can you determine the genotype of an unknown?

A

Test cross

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34
Q

The frequency of the hybrid recessive allele=

A

Frequency of the recessive Phenotype

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35
Q

The Frequency of the hybrid dominant allele=

A

Frequency of the dominant phenotype

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36
Q

In a Mendelian cross, the F1 generation

A

Will consist exclusively of heterozygotes displaying the dominant phenotype for the allele combination in the locus in being examined.

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37
Q

F2 Generations shows

A

Shows the outcome of the segregation of alleles in the F1 Gametes.
F2 will show all of the possible phenotypes.

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38
Q

9:3:3:1

A

Phenotypic proportions in F2 of a dihybrid cross.
9(double dominance)
3(single dominance)
3(single dominance)
1(recessive)

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39
Q

Parental phenotypes

A

Phenotypes seen in P0

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40
Q

Recombinant Phenotypes

A

Phenotypes not seen in parents or F1

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41
Q

The Second Mendelian Law

A

Law of Independent Assortment.
Simply the first law applied to alleles of two or more genes: simply multiplying the monohybrid ratios.
Applies not only to dihybrid crosses, but for any number of genes.

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42
Q

Law of Independent Assortment

A

Alleles of two (or more) genes (loci) segregate independently during transmission from parent to offspring.
The two dominant phenotypes appear at 100% in the F1 (hybrid genotype).
In F2, 4 phenotypes are present.
The expected F2 frequency for phenotypes generated by alleles of two loci is: 9:3:3:1 (double dominant:dominant recessive:recessive dominant:double recessive

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43
Q

In the F2, 4 phenotypes are present:

A

Two parental phenotypes present in the P0 generation.
Two new phenotypes (recombinants) absent from P0 or F1.

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44
Q

Does the arrangement of alleles in the P0 affect the F1?

A

no

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45
Q

Does the arrangement of alleles in the P0 affect the F2?

A

no

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46
Q

Hypothesis

A

an idea to test

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47
Q

Data

A

Collection of observations or experimental data specifically planned to test the hypothesis

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48
Q

The Chi-Square (X^2) test

A

Tests whether the sample collected (peas counted) can be used to support a hypothesis. (expected mendelian ratio).
Often this will test against the hypothesis (null hypothesis)

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49
Q

Null Hypothesis

A

There is no difference between the observed phenotypic ratio and the expected ratio.

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50
Q

Steps for Chi-square test

A

1: do the experiment and count the observed numbers.
2:predict expected numbers based on hypothesis.
3: calculate how well the data fit our hypothesis.
4: determine the degrees of freedom.
5: accept or reject our hypothesis. Compare your X2 to the critical value. Compare P-value to significance level.

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51
Q

Expected number

A

Total # offspring counted x expected frequency

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52
Q

X2

A

=Sum (observed-expected)^2/expected

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53
Q

Degrees of freedom (df)

A

Number of phenotypic classes e.g. 4-1
A measure of how many ‘types’ of data are being used relative to how much information you are trying to learn.
Bigger df means your results are more likely to be representative.

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54
Q

X2<critical

A

not significant

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55
Q

Reject null hypothesis

A

There is a significant difference between the observed phenotypic ratio and the expected ratio.

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56
Q

The Multiplicative Rule

A

If the events A and B are independent, the probability that they will occur together, P(A and B) is: P(A) x P(B)=

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57
Q

The Additive Rule

A

If the events A and B are independent, the probability that only one of them occurs, denoted P(A or B), is: P(A)+P(B)- [P(A) xP(B)]
If the two events do not overlap in the sample space, they are said to be mutually exclusive.

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58
Q

Mendel’s Law create predictions

A

If alleles segregate at random during gamete formation, and fertilization is also random, offspring ratios should follow rules of probability.

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59
Q

probability of two independent events happening together (A and B)

A

Probability of 1st event multiplied by the probability of the 2nd event.
P(A) x P(B)

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60
Q

Probability of a particular genotype (in offspring)(Y and y)

A

Probability of obtaining a particular allele in the male gamete X probability of obtaining a particular allele in the female gamete.
P(Y) x P(y)

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61
Q

Human genome

A

23 pairs of chromosomes (2n=46)
22 pairs of autosomes (homologous chromosomal pairs); expected diploid mendelian inheritance.
1 pair of sex chromosomes (X and Y), which are not allele; causes very different inheritance patterns (non-mendelian)

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62
Q

Obstacles to Human Genetic Analysis

A

Incomplete family records
Small number of progeny
Uncontrolled environment- eg Phenotypic plasticity

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63
Q

mendelian Principles in human genetics

A

Wildtype=normal=healthy
Affected=Diseased=mutant
Not all low frequency human alleles are bad- i.e. red hair.
This is not a judgement on the condition
These terms are relative to the majority of humans

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64
Q

Pedigrees

A

Are diagrams that show the relationships among the members of a family.
They represent the inheritance pattern of a specific character/condition

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65
Q

Pedigree analysis predicts genotypes

A

Parents aren’t affected so trait must be recessive.
Homozygous would be mean affected parents.
Parents are heterozygous

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66
Q

Inheritance of a Recessive Trait

A

Recessive traits may occur in individual whose parents are not affected. (not true for dominant traits, ‘skipping’ generations)
Recessive traits often occur rarely in a pedigree.
Recessive allele hidden in heterozygotes.(‘carrier’ notation)
Rare recessive traits are most likely to appear in a pedigree when spouses are related to each other.

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67
Q

Recessive Mutations

A

Most common causes of human genetic diseases.
Individuals with the disease are homozygous for the recessive allele.
Recessive alleles usually lack function= NULL (illegible DNA ‘instructions’, fail to make a product/protein- or make a non-functional product)

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68
Q

Interpretation of pedigrees

A

often a pedigree is consistent with only a particular mode of inheritance (dominant or recessive).

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69
Q

Rules for interpretation of pedigrees

A

dominant trait- unaffected parents can’t have an affected child.
recessive trait- unaffected parents can have an affected child

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70
Q

Guidelines of interpretation of pedigrees

A

Dominant trait- tends to appear in every generation
Recessive trait- tends to skip generations.

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71
Q

If a genetic condition is rare

A

It will be present in very few families in a population.
Unaffected individuals that marry into the family with the conditions, are likely homozygous for the normal allele rather than heterozygous.

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72
Q

Human Example: Albinism

A

recessive
Albinism- deficient pigmentation- inability to produce melanin (most often due to lack of active tyrosinase)
A= normal allele- active tyrosinase
a=mutant allele- inactive tyrosinase
A/A=makes tyrosinase- melanin
a/a= no active tyrosinase-no melanin- albine
A/a=same phenotype as A/A genotype; one A allele is sufficient to produce adequate melanin

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73
Q

Cystic Fibrosis

A

A common human recessive disease.
Serious disease caused by a nonfunctional CFTR gene. (cystic fibrosis transmembrane conductance regulator)
Defective Cl transport causes thick mucus to build up in lungs.
1 in 2500 affected among Caucasians.
Individuals who have the disease (cc) rarely reproduce, but heterozygous carriers are common among Caucasians (1:20)
Recessive

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74
Q

Autosomal Dominant Traits

A

Are caused by a mutant allele that is dominant over the normal allele.
Such mutations are not as common as recessive, lack-of-function mutations.

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74
Q

Inheritance of a dominant trait

A

Every individual who carries the dominant allele manifests the trait. (unaffected individuals (dd) cannot be carriers)
Every affected individual is expected to have at least one affected parent. (the trait tends to show up in every generation).
If both parents are heterozygotes (Dd), they will be affected, but they can have normal children.

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74
Q

Cystic Fibrosis Probability

A

Cc x Cc= 1/4 probability of CC (unaffected), 1/2 probability of Cc (unaffected), 1/4 probability of cc (affected)

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75
Q

Autosomal Dominant Traits- Due to

A

Production of too much of a normal protein.
One functional copy of a gene does not make enough gene product.
Production of abnormal variant of a protein that interacts incorrectly with the normal protein or with some other structure in the cell.
Production of protein with some entirely new function or normal function in new place (gain-of function)

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76
Q

Determine Likely inheritance

A

By exclusion: is it recessive? When a trait is rare, you assume other families do not cary it. Can’t be recessive.
Is it dominant? Yes appears in every generation.
Is it sex linked? no, equally in males and females.

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77
Q

Achondroplasia

A

A dominant form of dwarfism.
Wild type gene (d) encodes a fibroblast growth factor receptor (FGFR-3), regulates chondrocyte proliferation and long bone growth.
Mutant allele (D) produces to much FGFR-3 which causes reduced growth of long bones.

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78
Q

Achondroplasia Genotypes

A

Dd genotype- dwarfism phenotype
dd genotype- normal bone growth
DD- lethal

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79
Q

Chromosome

A

Single strand of DNA in the nucleus

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80
Q

Chromatid

A

1/2 of replicated chromosome, attached together at the centromere in X shape

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81
Q

Sister Chromatids

A

Identical copies (diploid)
Same genes in same order
Same alleles in same order

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82
Q

Homologous chromosomes

A

Same chromosomes from different parents.
Same genes in same order
Homozygous- same alleles in same order
Heterozygous- different alleles in same order

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83
Q

What biological processes explain Mendelian Laws?

A

First law: meiosis
Second law: meiosis

84
Q

Mitosis

A

1 diploid cell- 2 identical diploid cells

85
Q

Meiosis

A

1 diploid cell- 4 different haploid cells (gametes)

86
Q

Chromosomal basis for mendel’s first law

A

Different alleles of the same gene segregate independently when homologous chromosomes seperate in Meiosis I.

87
Q

Chromosomal basis for mendel’s second law

A

Different genes segregate independently when different chromosomes seperate in Meiosis I.
4 possible gametes: Ab, AB, ab, aB

88
Q

Drosophila melanogaster

A

the canonical genetic model organism

89
Q

Cross WT x white eye (w)

A

100% dominant phenotype

90
Q

Sex influences expression of the mutant eye phenotype

A

Sex is associated with eye: not independent segregation.
w gene is on the X chromosome
Males are hemizygous (1X and 1Y chromosome)
Only 1 copy of w is required for white eyes in males.

91
Q

Genes for eye colour and sex

A

are co-segregating.
Defies mendel’s law

92
Q

Unit of segregation

A

Chromosomes which carry genes

93
Q

SRY

A

is a sex determining gene
Transcription factor
Activates other genes to develop testes
Part of a cascade of several genes

94
Q

Androgen insensitivity syndrome

A

X-linked dominant- gene present on X chromosome
Dysfunctional androgen receptor:cells cannot respond to androgens
Affected XY people may have female external genitalia or present as intersex
XX people are carriers with generally no phenotype

95
Q

Sex in Drosophila

A

Sex determination is based on the ratio of X chromosomes to sets of autosomal (A) chromosomes

96
Q

X-linked recessive rules (in humans)

A

(hemophilia, red-green colorblindness)
Nearly all affected people are male: all his daughters are carriers, no sons will be affected.
Carrier females are usually phenotypically normal but are heterozygous: half her sons are affected, half her daughters are carriers
All sons of an affected females will be affected

97
Q

The chromosome theory of inheritance

A

A cytological explanation to Mendel’s ratios.
Introduces the concept of sex dtermination and sex linkage
Marks the birth of cytogenetics

98
Q

Chromosome

A

single strand of DNA in the nucleus

99
Q

Chromatid

A

1/2 of replicated chromosome, attached together at the centromere of X in shape

100
Q

Sister chromatids

A

identical copies (diploid)
Same genes in same order
Same alleles in same order

101
Q

Homologous chromosomes

A

Same chromosomes from different parents
Same genes in same order

102
Q

Mendelian First law Biological process

A

Alleles of a single gene segregate independently from each other.
Why? Meiosis

103
Q

Mendelian Second Law biological process

A

Alleles of different genes segregate idependently from each other.
Why? Meiosis

104
Q

Mitosis

A

1 diploid cell- 2 identical diploid cells

105
Q

Meiosis

A

1 diploid cell- 4 different haploid cells (gametes)

106
Q

Chromosomal Basis for Mendel’s first law:

A

Different alleles of the same gene segregate independetly when homologous chromosomes seperate in Meiosis I

107
Q

Chromosomal Basis for Mendel’s Second Law

A

Different genes segregate independently when different chromosomes seperate in Meiosis I
4 possible gametes: Ab, AB, ab, aB

108
Q

Humans

A

23 pairs of homologs, 2n=46

109
Q

Drsophila melanogaster

A

The canonical genetic model organisms
Fruit fly
Thomas H. Morgan

110
Q

What type of inheritance does the white=eye allele have?

A

Prediction: the white-eye phenotype follows Mendel’s laws

111
Q

Cross WT x white eye (w)

A

get the red eye
100% dominant phenotype

112
Q

Female red eye (WT) x white eye male

A

Red eye offspring (WT)
100% dominant phenotype

113
Q

Male red eye (WT) x female white eye

A

offspring are female red eye (WT) and male white eye
1:1 eye ratio
sex linked

114
Q

How does sex influence expression of the mutant eye phenotype?

A

Sex is associated with eye colour: not independent segregation.
w gene is on the X chromosome
Males are hemizygous (1X and 1Y chromosome)
Only 1 copy of w is required for white eyes in males

115
Q

The white eye gene is not ‘assorting’

A

eye color is physically linked to sex

116
Q

Unit of segragation

A

Chromosomes which carry genes

117
Q

Red-green color blindness

A

Recessive X-linked
Mainly found in men, common (10% of male population)

118
Q

Duchenne Muscular Dystrophy (DMD)

A

A rare X-linked recessive muscle disorder where patients get progressively weaker

119
Q

X-linked dominant (Vitamin D-resistant rickets)

A

Affected males transmit the trait to all of their daughters but to none of their sons.
Affected heterozygous females transmit the trait to 1/2 of their children, regardless of sex (like autosomal dominant)
Affected homozygous females transmit the trait to all their children.
Because females can be heterozygous or homozygous, more females have the trait than males

120
Q

KAryotype

A

A collection all chromosomes (with specific number and structure) of a species/individual in a condensed state

121
Q

Cytogenetics-using karyotypes

A

Staines identify specific chromosomes and allow analysis
Done while chromosomes are bound up for mitosis

122
Q

Diploid

A

2n
Normal for most eukaryotes

123
Q

Monoploid

A

1n
The number of unique chromosomes in a set

124
Q

Haploid

A

1n
Only 1 set of chromosomes, no homologous chromosomes
E.g. Male bees, gametes

125
Q

Hemizygous

A

only for haploid organisms or sex chromosomes

126
Q

Euploid

A

Having a ‘normal’ number of each chromosome

127
Q

Polyploid

A

extra copies of each chromosome
Common in plants
common in certain tissues
Causes larger cells and increase cellular metabolism=transcription

128
Q

Triploid

A

3n

129
Q

Tetraploid

A

4n

130
Q

Polyploid organisms

A

Possible because relative gene dosage is preserved
Widespread in plants
Less common in animals- flatworms, leeches, shrimp, lizards, snails

131
Q

Advantages of Polyploidy

A

Lowers chance of inbreeding risk-buffered against deleterious alleles
Lessen selection on individual gene copies- gene function diversification
Associated with asexual reproduction-mechanism unclear

132
Q

Allopolyploid

A

Mixing two uneven genomes via hybridization
Example: brassica hybrids
Combination of allopolyploidy and chromosome loss or gain creates new species

133
Q

Autopolyploid

A

Multiplication of chromosomes from the same organism
1) bigger plants=bigger fruit and flowers
2) seedless plants-sterile

134
Q

‘Polyploidization’ events

A

Underlined evolution of flowering plants- whole genome duplication

135
Q

How are autopolyploids generated?

A

Natural
Artificial

136
Q

Natural autopolyploids generated

A

Mistakes during meiosis
A failure of one of the meiotic divisions produces a gamete with twice as many chromosomes (2n gametes)
Can be identified via karyotyping

137
Q

Artificial Autopolyploids generated

A

Treat meiotic or mitotic cells with microtubule inhibitor (i.e. colchicine) to arrest cells in metaphase.
Look for viable progeny (gametes) or plant tissue (for vegetative growth=cuttings)

138
Q

How are allopolyploids generated?

A

Naturally or induced
Usually sterile

139
Q

Naturally or induced Allopolyploids generated

A

Are formed by hybridization: crosses between two related species

140
Q

Usually sterile allopolyploids generated

A

Horse x Donkey= sterile mule
Number and type of chromosomes matter

141
Q

Polyploid tissues are important for normal physiology

A

In some tissues, cells replicate the DNA (s-phase) but do not divide: polyploid tissue in an otherwise euploid organism
Polyploidy can be a mechanism of selectively increasing cell volume and/or cell metabolism

142
Q

Polyploidy tissues in humans

A

Liver- hepatocytes, 16n
Heart- cardiomyocytes, 4-8n
Vascular system-smooth muscle cells
Bone marrow- (megekaryocytes, platelet producing cells), 64 n
Skin- keratinocytes, 12 n

143
Q

Agricultural advantages and generation of monoploids

A

Monoploid organisms can be used in research for:
Screening genotypes for useful mutations

144
Q

Non-disjunction

A

improper chromosome segregation during meiosis

145
Q

Non-disjunction during meiosis

A

Rare, often lethal
Gametes have an incorrect number of chromosomes

146
Q

Non-disjunction of the X chromosomes produces (in flies)

A

Rare white-eyed female (XXY) in F1: normally only males (XY) carry the white mutation.
Rare viable red eye males (X0) that lack the Y chromosome.
It is the dosage of X chromosomes in the genotype, not the presence of the Y, that determines sex

147
Q

Loss of genetic material

A

Typically affects one gene
Large-scale chromosome changes= chromosome mutations: affect many genes. ;eads to structural differences that can be detected using a microscope

148
Q

Aneuploid

A

Abnormal number of one or more chromosomes, but not all
Caused by non-disjunction
Homologs don’t seperate in meiosis.
Monosomic
Trisomic

149
Q

Monosomic

A

One missing chromosome
2n-1
X0 sex determination- bees, some bats, most spiders, some snails…
All are lethal in humans except X0 (turner syndrome)

150
Q

Trisomic

A

One extra chromosome compared wild type- 2n+1
Most are lethal in humans except: Klinefelter syndrome (XXY), Jacob syndrome (XYY)-few symtoms, Trisomy X (XXX)-few symptoms, Down syndrome (trisomy 21)

151
Q

Karyotype of Down syndrome

A

Trisomy 21

152
Q

Down Syndrome (trisomy 21)

A

Genotype: 45 XX or XY
Stereotypical facial structure and neurological issues
Frequency from 1:2,000 un young mothers to 1:50 in “older” mothers
Most cases are sporadic, not heritable: caused by chromosome nondisjunction

153
Q

Trisomies increase in frequency with increased maternal age

A

All oocytes are present at mother’s birth: oocytes arrest in Meiosis I, ageging in the ovaries.
Meiosis I continues upon fertilization.
During ageging the association between homologs weakens: increased chance of non-disjunction with age

154
Q

Trisomies for other chromosomes are often incompatible with development, lead to miscarriages

A

Actual numbers of aneuploidy is unknown from miscarriages before the pregnancy is known.
Only least serious forms survive to birth: other chromosomes have too many critical genes

155
Q

Gene dosage

A

The amount of a gene product is dependent on how many copies of the gene there are.
The products of genes typically do not work in isolation
Gene imbalance is not enough to be lethal

156
Q

The effect of chromosome size

A

Large chromosomes generally have more genes- greater chance of imbalance that is essential for embryonic development

157
Q

Relocation of genetic material

A

Bigger chromosomal changes: affect more genes
more likely to impact phenotype
More likely to impxct meiosis

158
Q

Non-viable rearrangements

A

Too damaged
Lacks correct number of centromeres: chromosomes can’t seperate properly in mitosis
Lack correct arrangement of telomeres: terminal genes will be eroded in further rounds of mitosis
Loss of required genes or severe impairment of gene function

159
Q

Unbalanced rearrangements:

A

Changes gene number. Deletions and duplication inolving at least one gene

160
Q

Balanced Rearrangements

A

No change in gene and centromere number.
Inversions and reciprocal translocations that change gene order

161
Q

Chromosomal translocations

A

often silent.
are the most common chromosomal rearrangements in humans, 0.4% of individuals contain at least one translocation

162
Q

Williams Syndrome

A

Phenotype: developmental delays and learning disabilities. Distinct facial features, highly soical personlaities, musical talent and strong language skills.
Genotype: deletion of 27 genes on chromosome 7. Deleted section flanked by 2 repeats, increasing the likelihood of mismatch during cross-over.

163
Q

HEMIZYGOUS

A

A gene or set of genes that do not have a matching allele on a homologous chromosome
1. Most common for sex chromosomes
2. Can also occur with large scale chromosome arrangements

164
Q

Intraallelic effects

A

Between alleles of the same gene,

165
Q

Haplosufficient

A

genes that only require 1 copy to affect the phenotype= Dominant
Example- Albinism: only 1 copy of functional tyrosinase needed to make melanin. Heterozygotes still get melanin= not albino

166
Q

Haploinsufficient

A

Genes that requires more than 1 copy to affect the phenotype= recessive
Example: Achondroplasia dwarfism
Mutations are often dominant

167
Q

Null allele

A

non functional

168
Q

Allelic series

A

describes the dominance hierarchy of multiple alleles

169
Q

Hypomorphic allele

A

has partial function

170
Q

Incomplete dominance

A

Appearance of a third phenotype that ‘blends’ two parental ones.
No clear dominance in the heterozygote.
New phenotype not present in parents.

171
Q

Codominance

A

More than one allele is dominant.
Heterozygote displays both parental phenotypes: variegation

172
Q

Incomplete dominance in humans

A

often quantitative traits respoding to a single genetic locus have incomplete dominant alleles.
Skin pigmentation (melanin production levels)

173
Q

Codominance in humans:

A

ABO blood type

174
Q

Pleiotropy

A

one allele, affecting two or more phenotypes

175
Q

Chimeric gene

A

produced from the fusion of 2 genes

176
Q

Retinoblastoma:

A

only 75% of the poeple who carry the dominant mutant allele develop cancer

177
Q

Polydactyly:

A

50-80% of the people who carry the dominant mutant allele develop malformations

178
Q

Variable (incomplete) penetrance

A

Individuals with the same genotype may or may or may not express the phenotype.
Same genotype, different (normal x mutant) phenotypes

179
Q

What determines penetrance of the phenotype?

A

Modifier genes
Environmental factors
Allelic variation-similar but not identical alleles
Complex interactions of the above: genotype x environment

180
Q

Variable expressivity

A

The degree or intensity with which a genotype is expressed (100% of individuals show the consequences of the mutation at the phenotypic level, but there are many possible degrees of ‘severity’) same genotype, variable (non-uniform) mutant phenotypes

181
Q

Marfan syndrome

A

Autosomal dominant disorder
Tsll individuals, long limbs, fingers
Mild cases: nearsightedness
Severe cases: aorta, skeletal malformations
Mutation in the FBN1 gene that codes to FiBRILLIN-1 an important proteins for connective tissue integrity

182
Q

Neurofibromatosis

A

Variable penetrance+ Variable expressivity
50% to 80% of the individuals carrying the dominant mutant allele develop variable forms of the diseases

183
Q

Polygenic Inheritance

A

many genes (and alleles), affecting
Opposite: monogenic- a trait is only affected by 1 gene
Height, skin color, weight, behavioral phenotypes are often polygenic.
Incremental effect on phenotype

184
Q

Polygenic trait

A

Many genes contribute to a single effect
1 phenotype, multiple genes

185
Q

Pleiotropy

A

A gene has multiple effects
1 gene many phenotypes

186
Q

How alleles at different loci interact with one another

A

Additive gene action
Complementary gene action
Duplicate gene action
Dominant epistasis
Recessive epistasis

187
Q

Gene interactions

A

Metabolic pathways controlling specific phenotypes

188
Q

No gene interaction

A

2 loci, 2 traits, 4 phenotypes

189
Q

Additive gene action

A

2 loci, 1 trait, 4 phenotypes
Phenotypic ratio 9:3:3:1

190
Q

Complementary gene action

A

2 loci, 1 trait, 2 phenotypes

191
Q

Redundancy (duplicate gene action)

A

2 loci, 1 trait, 2 phenotypes

192
Q

Redundancy

A

Modified phenotypic ratio 15:1
The dominant alleles of both genes produce the same phenotypic effect

193
Q

Epistasis

A

The phenotype of a gene masked by alleles of another gene.
An allele of one gene overrides the phenotypic effect of an allele of another gene.

194
Q

In Drosophila

A

The white mutation produces white eyes.
The cinnabar mutation in a different gene produces bright red eyes.
When both mutations are present in the same fly the eyes are white.
The white mutation is epistatic to the cinnabar mutation.
The cinnabar mutation is hypostatic to the white mutation.

195
Q

Recessive Epistasis

A

When the recessive allele of one gene masks the effect of the second gene (dominant or recessive)
2 loci, 1 trait, 3 phenotypes
Ex: labrador coat color
Modified phenotypic ratio 9:3:4

196
Q

Dominant epistasis

A

When the dominant allele of one gene masks the effect of the second gene (dominant or recessive)
2 loci, 1 trait, 3 phenotypes
Ex: squash colour
Modified phenotypic ratio 12:3:1

197
Q

Functional interactions between gene products (porteins)

A
  1. Enzymes in a metabolic/synthesis pathway
  2. Proteins in a signaling pathway
  3. Proteins in a gene regulation pathway
198
Q

Reject null hypothesis

A

There is a significant difference between the observed phenotypic ratio and the expected ratio.
These data cannot be explained by a Mendelian dihybrid cross/

199
Q

Crossing over

A

The cellular mechanism that generates recombination

200
Q

Chiasmata

A

Sites of crossing over

201
Q

Recombination

A

a new combination of alleles.
Usually refers to a new combination of alleles of linked genes on the same chromosome

202
Q

Frequency of Recombination

A

% chance of crossing over during meiosis between specific loci

203
Q

No cross over

A

no genetic recombination
outcome 100% parental gametes
# of chromatids involved: 0/4

204
Q

Cross over before DNA duplication

A

of chromatids involved: 4/4
Outcome 100% recombinant gametes

205
Q

Cross over after Meiosis I

A

of chromatids involved: 4/4
Outcome: 100% parental gametes

206
Q

Cross over happens in Meiosis I

A

Half of the gametes are recombinant.
Balances variation with stability
# of chromatids involved: 2/4
Outcome: 50% parental gametes, 50% recombinant gametes

207
Q

How often does crossover happen?

A

Crossing over at a specific locus is RARE
but common on average during meiosis across all chromosomes

208
Q

Still used today

A

Selective breeding
Human genetic disease mapping

209
Q

Recombination Frequency (RF)

A

The distance between two markers on a chromosome is directly related to how often crossover events occur between them.
=The percentage of offspring that are recombinant
RF=number of offspring with recombinant genotypes/total number of offspring

210
Q

Synteny

A

genes on the same chromosome= syntenic genes

BIO 226 (4 decks)

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