Lesson 11 Quantitative Genetics

Question 1

Discontinuous traits

Answer 1

Traits that fall into discrete categories

Question 2

Quantitative traits

Answer 2

Show a continuum of phenotypic variation within a group of individuals

Question 3

variance

Answer 3

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

Question 4

What does variance help us understand?

Answer 4

Genetic variation in a population

Question 5

Standard deviation

Answer 5

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

Question 6

correlation

Answer 6

statistic that can compare the degree of association between two variables

Question 7

Polygenic inheritance

Answer 7

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

Question 8

Quantitative trait loci (QTLs)

Answer 8

Locations on chromosomes where the genes reside that influence quantitative traits

Question 9

Experiment 24A: polygenic inheritance

hypothesis

Answer 9

DDT resistance is a polygenic trait

Question 10

Experiment 24A: polygenic inheritance

Starting materials

Answer 10

A DDT resistant and a DDT sensitive strain of fruit flies

Question 11

Experiment 24A: polygenic inheritance

protocol

Answer 11

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

Question 12

Experiment 24A: polygenic inheritance

Interpreting the data

Answer 12

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.

Question 13

What is used to map QTLs?

Answer 13

RFLPs and other molecular markers

Question 14

What is the basis of QTL detection?

Answer 14

The association between genetically determined phenotypes and molecular markers such RFLPs

Question 15

RFLP mapping strategy

Answer 15

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.

Question 16

Heritability

Answer 16

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

Question 17

What is phenotypic variance due to?

Answer 17

Additive effects of genetic variance and environmental variance

Question 18

True heritability in the broad sense

Answer 18

Hb^2 = Vg/Vt

Takes into account all genetic factors that could affect the phenotype

Question 19

What do geneticists divide Vg into?

Answer 19

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

Question 20

What variance do geneticists focus on the most?

Answer 20

Va

Question 21

Narrow-sense heritability

Answer 21

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

Question 22

Experiment 24B: human fingerprints

hypothesis

Answer 22

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.

Question 23

Experiment 24B: human fingerprints

Starting materials

Answer 23

A group of human subjects from Great Britain

Question 24

Experiment 24B: human fingerprints

protocol

Answer 24

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

Question 25

Experiment 24B: human fingerprints | Interpreting the data

Answer 25

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

Question 26

triradius

Answer 26

Triple junction in fingerprint

Question 27

arch

Answer 27

No triradius

Question 28

whorl

Answer 28

Two triradii

Question 29

Bonnevie's method of counting

Answer 29

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.

Question 30

When are heritability values relevant?

Answer 30

To particular groups raised in a particular environment

Question 31

Selective breeding

Answer 31

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.

Question 32

Realized heritability

Answer 32

``` 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 ```

Question 33

Response in offspring

Answer 33

R = meanXoffspring - mean of starting population

Question 34

Selection differential

Answer 34

S = mean of parents - mean of the starting population

Question 35

heterosis or hybrid vigor

Answer 35

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

Question 36

Two hypothesis to explain heterosis

Answer 36

1. Dominance hypothesis | 2. overdominance hypothesis

Question 37

Dominance hypothesis

Answer 37

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.

Question 38

overdominance hypothesis

Answer 38

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