Topic 9 part 3 (Migration and gene flow)

Question 1

Gene flow

Answer 1

movement of individuals from one population to another, and subsequent mating

-general impact: reduces the level of population differentiation (as measured by Fst, etc)

Question 2

Continent-Island model (of migration)

Answer 2

• assumes ONE way migration from a large continental pop’n to a small island pop’n
• it can also be adapted to other situations where gene flow is unidirectional

Question 3

Island Model (of migration)

Answer 3

describes the case where a large number of islands randomly exchange individuals

• islands can represent: actual islands, lakes, fragments of habitats, mountains separated by valleys, etc.
• assume no genetic drift (by assuming pop’s on islands are infinitely large)
• good model for organisms that can move very easily from place to place
• ->equal prob. that any pop’n exchanges migrants w/ any other pop’n

Question 4

Stepping Stone Model (of migration)

Answer 4

-accounts for the fact that adjacent pop’ns are much more likely to to exchange migrants than more distant pop’ns

Question 5

Isolation by distance (pattern)

Answer 5

in this pattern, geographic distance is correlated to genetic distance

1. the greater the geog. distance, the greater the genetic diff b/w islands
2. the smaller the geog. distance, the smaller the genetic diff b/w islands

-continuously distributed organisms: can also exhibit isolation by distance pattern

Question 6

Effect of migration on HW principle

Answer 6

• movement of migrants into a pop’n can change the alleles frequencies
• initially cause HW disequ’m
• one round of random mating restores HW eq’m (based on new allele freq’s)

Question 7

Effect of migration on Gametic Disequilibrium

Answer 7

-Diseq’m may never break down if you continuously introduce migrants

• consider a pop’n with only AAbb, and you introduce aaBB
• results in Dmin (non-random genotypic associations among the loci)
• AAbb and aaBB are only able to produce repulsion phase gametes

Question 8

Migration and Genetic Drift

Answer 8

• drift and migration oppose each other

- drift causes pop’s to diverge and gene flow acts to homogenize pop’s

Question 9

Infinite Islands Model (of migration)

Answer 9

• finite population sizes, but the number of islands is infinitely large
• assumes the same effective population size on each island

Question 10

Migration and drift (with infinite islands model)

Answer 10

1. if gene flow is low, drift will be the dominant force on each islands and they will diverge
2. If gene flow is high, migration will be the dominant force