Lecture 29

Question 1

Traits to genes:

Answer 1

• ## We want to associate particular traits with particular genes

Question 2

Traditional trait analyses in ecological genetics:

Answer 2

• Focussed on morphological polymorphisms eg. the peppered moth and response to pollution levels
• Pretty snail with shells with different banding patterns, this is a polymorphism, some habitats have higher numbers of dense bands than other habitats

Question 3

Quantitative genetics:

Answer 3

• Focus on phenotype with continuously distributed variation (vs discrete)
• Study statistically
• Trait variation is assumed to be controlled by many genes, major and minor

Question 4

Why are quantitative traits important?

Answer 4

• most of the key characteristics considered by plant and animal breeders are quantitative
• Many of the traits that allow species to adapt to its environment are quantitative

Question 5

From discrete phenotypes to quantitative traits:

Answer 5

• Add intermediate categories and genes
• Add environmental effects
• The data will become less and less discrete, and will form a normal distribution

Question 6

Analysing quantitative traits:

Answer 6

• NS operates on differences between individuals in populations and is measured using variance

Question 7

Variation P =

Answer 7

variation G + variation E

Question 8

Phenotype P =

Answer 8

genotype G + environment E

Question 9

Measuring adaptive genetic diversity: Vp = (Va+Vd+Vl) +Ve

Answer 9

Where
- Va = additive genetic variance, determines resemblance between relatives across generations
- Vd = dominance variance - interactions within a locus, affects similarity between offspring (within generations)
Vi = epistasis variance - interactions between loci

Question 10

Additive gene action is the simplest model:

Answer 10

• Assume quantitative trait controlled by two loci (A and B), each having two alleles (A1, A2 and B1, B2)
• There is no interaction or dominance
• The 1 alleles contribute 1 and the 2 alleles contribute 2
• The effects of each allele add up in each genotype to determine the phenotype, they are additive

Question 11

A table with dominance will show

Answer 11

• Additive effects of genes
• A way to test dominance is to cross two traits together (aa and AA) if the Aa falls back a bit there must be additive inheritance

Question 12

Epistasis in Danaus chyssipus, a butterfly:

Answer 12

• eg) forewing size is largely determined by 2 loci showing both dominance and epistasis
• B dominant to b but this depends on the C genotype
• BB Bb are smaller when heterozygous at the C locus

Question 13

Measuring genetic diversity in quantitative traits:

Answer 13

• Heritability
• Narrow sense
• Broad sense

Question 14

Narrow-sense heritability:

Answer 14

• Proportion of phenotypic variance passed on to relatives

- Indicative of response to selection

Question 15

Broad-sense heritability:

Answer 15

• The degree of genetic determination of a trait

- h squared(broad) = Vg/(Vg + Ve)

Question 16

Heritability

Answer 16

Vp = (Va + Va + Vd + Vi) + Ve

Question 17

Heritability:

Answer 17

• Varies among traits
• Measure the ability to respond to selection
• Higher genetic variance (h squared) allows persistence under stronger environmental change

Question 18

Estimating heritability from family data:

Answer 18

• Plot family data on a scattergram of both parents
• We need the slop of the line of best fit (regression line)
• b = slope of the line of best fit (relates to heritability)
• b = h squared (mid parent offspring)
• b = 0.5h squared (one parent)
• Slope of 1 the trait is completely heritable