Topic 8: Genetic Drift

Question 1

what is genetic drift?

Answer 1

sampling error spread across generations
- chance fluctuations in allele freq due to random sampling of gametes each generation

Question 2

why does genetic drift violate assumptions of HW principle, despite not causing HW disequil?

Answer 2

randomly sampled gametes will randomly unite zygotes -> perfect HW equilibrium

HOWEVER, zygotes are based on the new allele freq after sampling error. It changes allele freq, thereby violating assumptions of the HW principle

Question 3

what do we expect for large population when it comes for genetic drift?

Answer 3

we don’t expect the mean to change!
just variance of mean of allele freq (bigger spread, but the avg is same)

Question 4

What does Fi mean?

Answer 4

fixation index;
probability that two randomly chosen alleles in a population will be identical by descent (or autozygous)

over time, genetic drift increases Fi;
smaller the pop, greater the increase in Fi

Question 5

What is Ne?

Answer 5

Effective Pop Size (Ne):
size of a pop with equal numbers of breeding males and females, panmictic, and constant pop size over time, with no variation in numbers of progeny contributed to next gen;

that will undergo reductions in heterozygosity at the same rate as our census pop size due to drift alone (autozygosity will increase at same rate)

Question 6

what contributes to reduction of Ne compared to census pop? (4)

Answer 6

1. # breeding individuals
2. unequal # males/females
3. variation in contributions to next gen in terms of # offspring among mating pairs
4. fluctuations in pop size over time

Question 7

drift and D: the smaller the pop size, the ____ the variance of mean value of D

Answer 7

larger

Question 8

relationship between drift and D

Answer 8

drift -> changes D in random and stochastic way