17 - Genetic Drift and Selection

Question 1

What are the assumptions of HWE?

Answer 1

• random mating
  
  • no assortative / disordered mating
  • no inbreeding
• no mutation
• no selection
• no drift
• no migration
• sexual, diploid, no overlapping generations

Question 2

What is assortative mating?

Answer 2

non-random mating based on similar phenotypes / genotypes

Question 3

What is the difference between assortative mating and inbreeding?

Answer 3

assortative - homozygosity at selected loci
inbreeding - homozygosity at all loci

Question 4

What is inbreeding depression?

Answer 4

homozygosity for deleterious recessive alleles

Question 5

How do you calculate the inbreeding coefficient?

Answer 5

F = 1 - (observed freq hetero) / 2pq (expected freq hetero)

Question 6

What is F = 0?

Answer 6

no inbreeding

Question 7

What is F = 1?

Answer 7

complete inbreeding

Question 8

What is genetic drift?

Answer 8

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

Question 9

What is the effect of genetic drift in a population with infinite size?

Answer 9

no effect

Question 10

What is the effect of genetic drift on a smaller population?

Answer 10

smaller population, larger effect

Question 11

What goes genetic drift ultimately lead to?

Answer 11

• unbiased fixation or loss of alleles
• divergence between populations

Question 12

When does selection happen?

Answer 12

• heritable genetic differences in a population
• genetic differences lead to phenotypic differences
• has an effect on survival and reproduction

Question 13

What is directional selection?

Answer 13

• increased or decreased value of the trait

Question 14

What is disruptive selection?

Answer 14

• extreme phenotypes are selected for

Question 15

What is stabilising selection?

Answer 15

• median selected for

Question 16

What is the letter assigned to fitness?

Answer 16

W

Question 17

What is the W of the genotype with the highest fitness?

Answer 17

W = 1

Question 18

How do you calculate relative fitness?

Answer 18

no. offspring / no. offspring of fittest

Question 19

What is the selection coefficient?

Answer 19

Tells us how strong selection is against a genotype relative to the most fit

S = 1 - relative fitness

Question 20

What is the outcome of selection?

Answer 20

• biased fixation or loss of alleles
• disruptive or stabilising selection

Question 21

How do you work out the frequency of a new allele?

Answer 21

Haploid
- number of allele / population size

Diploid
- number of allele / 2 x population size

Question 22

What is the effect of migration?

Answer 22

• 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