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Flashcards in Lesson 11 Quantitative Genetics Deck (38)
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1

Discontinuous traits

Traits that fall into discrete categories

2

Quantitative traits

Show a continuum of phenotypic variation within a group of individuals

3

variance

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

4

What does variance help us understand?

Genetic variation in a population

5

Standard deviation

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

6

correlation

statistic that can compare the degree of association between two variables

7

Polygenic inheritance

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

8

Quantitative trait loci (QTLs)

Locations on chromosomes where the genes reside that influence quantitative traits

9

Experiment 24A: polygenic inheritance
hypothesis

DDT resistance is a polygenic trait

10

Experiment 24A: polygenic inheritance
Starting materials

A DDT resistant and a DDT sensitive strain of fruit flies

11

Experiment 24A: polygenic inheritance
protocol

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

12

Experiment 24A: polygenic inheritance
Interpreting the data

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.

13

What is used to map QTLs?

RFLPs and other molecular markers

14

What is the basis of QTL detection?

The association between genetically determined phenotypes and molecular markers such RFLPs

15

RFLP mapping strategy

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.

16

Heritability

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

What is phenotypic variance due to?

Additive effects of genetic variance and environmental variance

18

True heritability in the broad sense

Hb^2 = Vg/Vt
Takes into account all genetic factors that could affect the phenotype

19

What do geneticists divide Vg into?

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

What variance do geneticists focus on the most?

Va

21

Narrow-sense heritability

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

Experiment 24B: human fingerprints
hypothesis

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

Experiment 24B: human fingerprints
Starting materials

A group of human subjects from Great Britain

24

Experiment 24B: human fingerprints
protocol

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

Experiment 24B: human fingerprints
Interpreting the data

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

26

triradius

Triple junction in fingerprint

27

arch

No triradius

28

whorl

Two triradii

29

Bonnevie's method of counting

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

When are heritability values relevant?

To particular groups raised in a particular environment