Lecture 8: Genetic drift

Question 1

Genetic Drift (4)

Answer 1

-the change in frequency of an existing gene variant in the population due to random chance

-strongest when sample size, i.e. population
size, is small

-Drift is random

– no allele or genotype favoured
Rare alleles tend to be under-sampled

Question 2

Effects of drift (2 notes and 2 effects)

Answer 2

Allele frequency in one generation affects
gamete pool for the next generation, leading to two major outcomes:

-loss of heterozygosity and fixation for a single allell

-differentiation among populations

These effects are most dramatic in small populations

Question 3

Effective population size

Answer 3

-Denoted as Ne

-The number of individuals that effectively participates in producing the next generation

Question 4

Population differentiation (5)

Answer 4

Fst (single locus) or Gst (multilocus) =

var(p) / pBar * (1-pBar)

where:
-pBar and qBar are the mean p and q of the examined populations

-and var(p) is the variance of p between the populations = (p pop1 - pBar)^2 + (p pop2 - pBar)…… / number of populations

-Will be between 0-1 with anything > than 25% meaning very high differentiation, and anything less than 5% being very low