Lecture 6/7

Question 1

Which evolutionary forces are deterministic?

Answer 1

1. Selection
2. Mutation
3. Migration

Question 2

What evolutionary forces are stochastic (randomly determined)?

Answer 2

4. Genetic drift

Question 3

What does genetic drift depend upon?

Answer 3

Genetic drift depends on the effective population size (drift is much stronger in smaller populations bc of larger fluctuations of allele frequencies)

Question 4

What is the definition of “island” distribution?

Answer 4

Restricted migration between islands, resulting in interbreeding between islands

Question 5

What is the definition of continuous distribution?

Answer 5

Unrestricted migration across population, resulting in ransom mating between within a breeding population (i.e. panmixia)

Question 6

What is the definition of genetic drift?

Answer 6

Random changes in the frequencies of alleles or genotypes in a population due to sampling error of gametes/genotypes in their contribution to the next generation

Question 7

What is the significance of genetic drift?

Answer 7

Drift has profound implications for evolution in populations that are fragmented; leads to differentiation of populations because changes in gene frequencies will progress independently in different populations, ultimately leading to fixation of 1 allele

Question 8

What is the definition of the founder’s effect?

Answer 8

The loss in genetic variation that occurs when a new population is established by a very small number of individuals from a larger population

Question 9

What is the definition of the bottleneck effect?

Answer 9

Occurs when the size of a population is dramatically reduced in some random event (e.g. natural disasters)

Question 10

What is the relationship between genetic drift and heterozygosity?

Answer 10

Genetic drift leads to a loss in heterozygosity as homozygosity increases

Question 11

What is the definition of effective population size?

Answer 11

(N_e) The size of a hypothetical population that would undergo the same loss in genetic diversity due to genetic drift as an actual population would under study

Question 12

What factors can reduce the effective population size?

Answer 12

1. Sex-ratio derivations
2. Mating systems
3. Fertility differences
4. Fluctuations in population size (N_e more affected by smaller population sizes than larger population sizes)

Question 13

How are selection and drift related?

Answer 13

Selection and drift depend on the strength of selection (magnitude of the selection coefficient) and the effective population size

Question 14

When does selection dominate?

Answer 14

4 N_e s >> 1 (larger population)

Question 15

When does drift dominant?

Answer 15

4 N_e s << 1 (smaller population)

Question 16

How does gene flow related to genetic drift?

Answer 16

Gene flow tends to oppose drift between populations

Question 17

What is the definition of gene flow?

Answer 17

The transfer of genetic variation from one population to another; tends to homogenize allele frequencies

Question 18

What happens to a population when there is very weak selection (s is near 0)?

Answer 18

Nearly Neutral Theory of Evolution: drift dominates when 4 N_e s << 1