17 - Genetic Drift and Selection Flashcards
What are the assumptions of HWE?
- random mating
- no assortative / disordered mating
- no inbreeding
- no mutation
- no selection
- no drift
- no migration
- sexual, diploid, no overlapping generations
What is assortative mating?
non-random mating based on similar phenotypes / genotypes
What is the difference between assortative mating and inbreeding?
assortative - homozygosity at selected loci
inbreeding - homozygosity at all loci
What is inbreeding depression?
homozygosity for deleterious recessive alleles
How do you calculate the inbreeding coefficient?
F = 1 - (observed freq hetero) / 2pq (expected freq hetero)
What is F = 0?
no inbreeding
What is F = 1?
complete inbreeding
What is genetic drift?
When only a subset of individuals contribute to the next generation
- event or pathogen kills others
- founder effect -> small group go and make their own population
What is the effect of genetic drift in a population with infinite size?
no effect
What is the effect of genetic drift on a smaller population?
smaller population, larger effect
What goes genetic drift ultimately lead to?
- unbiased fixation or loss of alleles
- divergence between populations
When does selection happen?
- heritable genetic differences in a population
- genetic differences lead to phenotypic differences
- has an effect on survival and reproduction
What is directional selection?
- increased or decreased value of the trait
What is disruptive selection?
- extreme phenotypes are selected for
What is stabilising selection?
- median selected for
What is the letter assigned to fitness?
W
What is the W of the genotype with the highest fitness?
W = 1
How do you calculate relative fitness?
no. offspring / no. offspring of fittest
What is the selection coefficient?
Tells us how strong selection is against a genotype relative to the most fit
S = 1 - relative fitness
What is the outcome of selection?
- biased fixation or loss of alleles
- disruptive or stabilising selection
How do you work out the frequency of a new allele?
Haploid
- number of allele / population size
Diploid
- number of allele / 2 x population size
What is the effect of migration?
- can add new alleles
- effect on frequency depends on how much migration, frequency of alleles in source population, frequency of alleles already in the population
