Lecture 29 Flashcards Preview

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Flashcards in Lecture 29 Deck (18)
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1
Q

Traits to genes:

A
  • ## We want to associate particular traits with particular genes
2
Q

Traditional trait analyses in ecological genetics:

A
  • 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
3
Q

Quantitative genetics:

A
  • Focus on phenotype with continuously distributed variation (vs discrete)
  • Study statistically
  • Trait variation is assumed to be controlled by many genes, major and minor
4
Q

Why are quantitative traits important?

A
  • 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
5
Q

From discrete phenotypes to quantitative traits:

A
  • Add intermediate categories and genes
  • Add environmental effects
  • The data will become less and less discrete, and will form a normal distribution
6
Q

Analysing quantitative traits:

A
  • NS operates on differences between individuals in populations and is measured using variance
7
Q

Variation P =

A

variation G + variation E

8
Q

Phenotype P =

A

genotype G + environment E

9
Q

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

A

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

10
Q

Additive gene action is the simplest model:

A
  • 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
11
Q

A table with dominance will show

A
  • 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
12
Q

Epistasis in Danaus chyssipus, a butterfly:

A
  • 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
13
Q

Measuring genetic diversity in quantitative traits:

A
  • Heritability
  • Narrow sense
  • Broad sense
14
Q

Narrow-sense heritability:

A
  • Proportion of phenotypic variance passed on to relatives

- Indicative of response to selection

15
Q

Broad-sense heritability:

A
  • The degree of genetic determination of a trait

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

16
Q

Heritability

A

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

17
Q

Heritability:

A
  • Varies among traits
  • Measure the ability to respond to selection
  • Higher genetic variance (h squared) allows persistence under stronger environmental change
18
Q

Estimating heritability from family data:

A
  • 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