Selection on Polygenic Characters Flashcards
How is variance in fitness measured? Simple and expanded versions.
Vp = Vg + Ve
Vp is phenotypic variance
Vg is genotypic variance
Ve is environmental variance
Vp= Va+Vd+Vi=Ve
Va is additive variance
Vd is dominance variance
Vi is epistatic variance
What is the difference between covariance and genotype by environment interactions for phenotypic variance?
Covariance is a correlation that can inflate or reduce phenotypic variation, i.e. habitat selection by different genotypes affects the phenotypic variance. GxE is an interaction, so different genotypes are affected by environmental variation in different ways.
What is additive genetic variance and what does it do? How is it measured?
The inheritance of a particular allele from your parent and this allele’s independent effect on the specific phenotype, which will cause the phenotype deviation from the mean phenotype.
h^2=Va/Vp
Heritability (h^2) can be determined from correlation between parents and offspring or from R=h2S by imposing artificial selection on a character, measuring R and S, and finding the realized heritability a posteriori.
What does heritability refer to and how is it measured?
Heritability refers to how much of the phenotypic variance is due to variance in genetic factors. Usually after we know the total amount of genetic variance that is responsible for a trait, we can calculate the trait heritability. Heritability can be used as an important predictor to evaluate if a population can respond to artificial or natural selection.
H^2=Vg/Vp
What is dominance variance?
Dominance genetic variance refers to the phenotype deviation caused by the interactions between alternative alleles that control one trait at one specific locus.
What is epistatic variance?
Epistatic variance involves an interaction between different alleles in different loci.
What is a selection differential?
The difference between the mean of a population and the mean of the individuals selected to be parents of the next generation.
How do you calculate response to selection?
R=h^2S
R is response to selection
h^2 is heritability
S is selection differential
Why does variation that reduces similarity (e.g. directional selection) between parents and offspring slow evolution?
Evolution depends on inheritance, so if inheritance is additive and directional selection causes rapid change, then genetic variation is reduced.
What is stabilizing selection?
Mean character is maintained at some intermediate value, aka intermediate form superiority.
What is disruptive or diversifying selection?
If two or more states of a characteristic are favored.
Draw stabilizing, directional and disruptive models given fitness, before frequency, after frequency effects on phenotype.
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What mechanism determines how each mode of selection will affect genetic variation?
Inheritance patterns.
Most characteristics vary under the influence of these two things.
Environment and several/many loci.
Is additivity more explanatory in general or is strong dominance and epistatis more explanatory? Does it change more slowly or faster than the alternative?
The latter, many characters that are correlated with fitness are controlled by these mechanisms.
These move more slowly than additive change.
