Population_genetics_part_II

Population_genetics_part_II - Population Genetics Part II...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Population Genetics Part II Reading: chapter 7 p 223-249, 264-268, 273-276 Ignore all Boxes
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Migration and the H-W principle
Background image of page 2
Migration (p 225) Movement of alleles between populations Gene flow Caused by anything that moves alleles from one population to another Long-distance dispersal Transport of pollen etc. by various sources Migration varies among different species Island populations are excellent “laboratories” for examining migration Figure 7.4, pg. 225 Can migration from the continent to the island shift allele frequencies from H-W equilibrium?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Can allele frequencies shift under migration? p226 Our mouse population has 2 Alleles: A 1 and A 2 Before migration the frequency of A 1 is 1.0 Will migration from the continent affect the allele frequencies? 1000 individuals –A 1 A 1 = 800/1000 = 0.8 –A 2 A 2 = 200/1000 = 0.2 After migration: Allele frequencies have changed Genotype frequencies are initially not consistent with H-W Expected H-W genotype frequencies: –A 1 A 1 = 0.64 (p 2 ) –A 1 A 2 = 0.32 (2pq) –A 2 A 2 = 0.04 (q 2 )
Background image of page 4
One round of random mating • Allele frequencies are now: A 1 = 0.8 and A 2 = 0.2 Random now mating occurs: p 2 + 2pq + q 2 = 1 (0.8) 2 + 2(0.8)(0.2) + (0.2) 2 = 1 0.64 + 0.32 + 0.04 = 1 A 1 A 1 = 0.64 (p 2 ) A 1 A 2 = 0.32 (2pq) A 2 A 2 = 0.04 (q 2 ) Our population is now back in H-W equilibrium What would happen if migration occurred again? It takes one round of random mating to restore HW equilibrium
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
An example: Lake Erie Water Snakes Example of migration from mainland to island Snakes vary in colour pattern which is determined by a single locus with two alleles Unbanded island snakes have a higher rate of survival than banded immigrants Selection favours unbanded snakes on the islands pg. 228
Background image of page 6
An example: Lake Erie Water Snakes cont. Why don’t the islands consist of only the unbanded snakes? Migration! It Prevents the island population from becoming fixed for the unbanded allele Migration can prevent the divergence of populations Figure 7.7, pg. 228 A= unbanded D= strongly banded
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
What is the effect of migration? In the case of the water snakes, migration maintains the banded snakes on the Islands, even though they have lower fitness (migration is working against selection in this example, but it could also do the opposite). Migration is a force that generally tends to homogenize populations
Background image of page 8
Migration and Homogenization Population 1 p= 0.1, q= 0.9 Population 2 p= 0.6, q= 0.4 Population 3 p= 0.4, q= 0.6 p = 0.3667, q = 0.6333 average allele frequencies among the three populations Migration generally acts to homogenize populations, or make their allele frequencies the same. If these three populations all
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/28/2011 for the course BIOL 301 taught by Professor Pickard during the Spring '09 term at Waterloo.

Page1 / 42

Population_genetics_part_II - Population Genetics Part II...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online