Lecture 10: Drift & Population Structure

Question 1

Define genetic drift

Answer 1

Changes in allele (and genotype) frequencies due to random sampling of breeding individuals in small (finite) populations

Question 2

What does genetic drift lead to?

Answer 2

• Loss of genetic variation (heterozygosity)
• Increase in homozygosity (inbreeding)
• fixation (or loss) of alleles
• change of genetic make up of the population (evolution)

Question 3

Define effective population size (Ne)

Answer 3

Number of breeding individuals contributing genes to next generation

Question 4

What are founder effects

Answer 4

the reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors. Loss of genetic variation, increase in homozygosity

Question 5

In what types (size) of populations is genetic drift strong or weak.

Answer 5

Genetic drift is strong in small populations and genetic drift is weak in large populations.

Question 6

What effect does the sex ratio have on the Ne?

Answer 6

Skewed sex ratio reduces Ne below census size

Question 7

How does population size fluctuation affect Ne?

Answer 7

The low points have a disproportionately large effect on reducing the effective population size below the average census size over the time interval. Why? After bottleneck you will loose alleles and genetic variation.

Question 8

Define population structure.

Answer 8

How is the variation partitioned within and among populations

Question 9

Understand migration-drift equilibrium

Answer 9

Migration homogenizes allele frequencies; drift differentiates allele freqeuncies

Question 10

Understand mutation-drift equilibrium

Answer 10

Mutation (u) introduces variation within population, drift (determined by Ne) eliminates it.