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Genetics > Lesson 11 Quantitative Genetics > Flashcards

Lesson 11 Quantitative Genetics Flashcards

1
Q

Discontinuous traits

A

Traits that fall into discrete categories

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2
Q

Quantitative traits

A

Show a continuum of phenotypic variation within a group of individuals

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3
Q

variance

A

Sum of squared deviations from the mean divided by the degrees of freedom (N-1)
Vx = sum(x -meanX)^2/N-1

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4
Q

What does variance help us understand?

A

Genetic variation in a population

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5
Q

Standard deviation

A

square root of variance. Helps up appreciate the amount of variation in a bell curve.

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6
Q

correlation

A

statistic that can compare the degree of association between two variables

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7
Q

Polygenic inheritance

A

Transmission of traits that are governed by two or more different genes

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8
Q

Quantitative trait loci (QTLs)

A

Locations on chromosomes where the genes reside that influence quantitative traits

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9
Q

Experiment 24A: polygenic inheritance

hypothesis

A

DDT resistance is a polygenic trait

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10
Q

Experiment 24A: polygenic inheritance

Starting materials

A

A DDT resistant and a DDT sensitive strain of fruit flies

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11
Q

Experiment 24A: polygenic inheritance

protocol

A
  1. Cross DDT-resistant strain to the sensitive strain. In each strain, chromosomes X, 2 and 3 were marked with alleles that provided easily discernible phenotypes.
  2. Take the F1 flies and backcross to both parental strains
  3. Identify the origin of the chromosomes in each fly according to their phenotypes
  4. Expose each fly to DDT on a filter paper for 18-24 hours
  5. Record number of survivors
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12
Q

Experiment 24A: polygenic inheritance

Interpreting the data

A

Some offspring obtained all three alleles from one parental strain, but most had a combination. The more from the DDT resistant strain, the more resistant. One allele alone did not offer maximal resistance.

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13
Q

What is used to map QTLs?

A

RFLPs and other molecular markers

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14
Q

What is the basis of QTL detection?

A

The association between genetically determined phenotypes and molecular markers such RFLPs

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15
Q

RFLP mapping strategy

A

Mate individuals that are very dissimilar with regard to their RFLP markers and are also different for quantitative traits. The experimenter then determines which RFLPs are segregating with the trait of interest.

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16
Q

Heritability

A

Amount of phenotypic variation within a group of individuals that is due to genetic factors
Hb^2 = Vg/Vt
Heritability squared = genetic variance/total variance

17
Q

What is phenotypic variance due to?

A

Additive effects of genetic variance and environmental variance

18
Q

True heritability in the broad sense

A

Hb^2 = Vg/Vt

Takes into account all genetic factors that could affect the phenotype

19
Q

What do geneticists divide Vg into?

A 
Vg = Va + Vd + Vi
A = variance due to additive alleles
D = variance due to alleles that follow a dominant/recessive pattern of inheritance
I = variance due to genes that interact in an epistatic manner
20
Q

What variance do geneticists focus on the most?

A

Va

21
Q

Narrow-sense heritability

A

Heritability of a trait due to the additive effects of alleles
hN^2 = Robs/Rexp
Robs is observed phenotypic correlation bet. Related individuals and Rexp is the expected correlation based on the known genetic relationship

22
Q

Experiment 24B: human fingerprints

hypothesis

A

Dermal ridge count has a genetic component. The goal of this experiment is to determine the contribution of genetics in the variation of dermal ridge counts.

23
Q

Experiment 24B: human fingerprints

Starting materials

A

A group of human subjects from Great Britain

24
Q

Experiment 24B: human fingerprints

protocol

A
  1. Take a person’s finger and blot it onto an inkpad
  2. Roll the person’s finger onto a recording surface to obtain a print
  3. With a low-power binocular microscope, count the number of ridges using the Bonnevie method
  4. Calculate the correlation coefficients between different pairs of individuals
25
Q

Experiment 24B: human fingerprints

Interpreting the data

A

Genetically unrelated individuals have a negligible correlation for this trait. Individuals who are genetically related have a substantially higher correlation.

26
Q

triradius

A

Triple junction in fingerprint

27
Q

arch

A

No triradius

28
Q

whorl

A

Two triradii

29
Q

Bonnevie’s method of counting

A

A line is drawn from a triradius to the center of the fingerprint. The ridges that touch this line are counted. The triradius ridge and the last ridge are not counted if the latter forms the center of fingerprint.

30
Q

When are heritability values relevant?

A

To particular groups raised in a particular environment

31
Q

Selective breeding

A

A practice in which a breeder chooses the individuals who possess traits that are desirable- from a human perspective - as parents of the next generation.

32
Q

Realized heritability

A 
Out of an artificial selection experiment can be used to estimate heritability in the starting population
hN^2 = R/S
hN^2 is realized heritability
R is response in the offspring
S is selection differential in parents
33
Q

Response in offspring

A

R = meanXoffspring - mean of starting population

34
Q

Selection differential

A

S = mean of parents - mean of the starting population

35
Q

heterosis or hybrid vigor

A

When two different inbred strains are crossed to each other, the resulting offspring are more vigorous than either of the inbred parental strains

36
Q

Two hypothesis to explain heterosis

A
  1. Dominance hypothesis

2. overdominance hypothesis

37
Q

Dominance hypothesis

A

Highly inbred strains have become homozygous fro one or more recessive genes that are somewhat deleterious (but not lethal). Because homozygosity happens as a matter of chance, two different inbred strains are likely to be homozygously recessive for different genes. When they are crossed with each other, the resulting hybrids are heterozygous and do not suffer the overdominance hypothesis.

38
Q

overdominance hypothesis

A

Proposes that heterosis is explained by the resulting hybrids being heterozygous for one or more genes that display overdominance

Genetics (12 decks)

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