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Biology 3300- Migration

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University of Lethbridge
BIOL 3300
Theresa Burg

Biology 3300 th Jan.27 Migration Movement of alleles between populations (gene flow) - Gene flow can happen at the gamete or individual level Dispersal of individuals or gametes - Internal vs external fertilization - Dispersal agents o Who or what is doing the dispersal and how they will impact gene dispersal - Barriers o Ex: water is a great dispersal barrier for birds  Many more birds on the mainland compared to islands  Travelling over greater distances over water is difficult for most birds o Some barriers will stop gene flow and others will facilitate it depending on the organism Have to have movement and reproduction to have impact on allele frequencies of the next generation Dispersal occurs only through adjacent populations (stepping-stone model) - Ex: Hawaiian Islands Island models allows for more 2D gene flow (rather than linear) - Assume all populations have same number of individuals (N) and equal migration rates (m) One Island Model - Asymmetrical migration - More space on the mainland has greater population - Island will have smaller population - There will be more movement from mainland to the island and less from island to mainland Two colonies of birds on separate islands - Pop. #1 has 7 Pop.#2 has 9 - #1 is fixed for yellow allele - #2 is homozygous for red allele - Migration of 3 yellow to red population - #1 R=0 Y=1 - #2 R= 18/24 = 0.75 (9 red individuals diploid (multiply by 2)) - #2 Y=6/24 = 0.25 - We have asymmetrical migration - Population 1 allele frequencies did not change - Population 2 allele frequencies changed quite a bit What are the predicted genotype frequencies under Hardy Weinberg? A 1 0.8 A1A 1 640 (0.8 *1000) p 2 A 2 0.2 A 1 2 320 (1000-(640+40)) 2pq A 2 2 40 (0.2 *1000) q 2 1000 What happens to the allele frequencies after one round of random mating? - Frequencies will stay the same We have to look at population size and number of migrants. Migration can change allele frequencies. The rate of change is proportional to: - Migration rate (what if 2RR, 3RY and 1YY move from pop. #1 to pop. #2?) - Direction of gene flow - Population differences in allele frequencies Before After P#1 P#2 P#1 P#2 RR 36 16 34 18 RY 48 48 45 51 YY 16 36 15 37 Before After R 1 0.6 0.6 Y 1 0.4 0.4 R 2 0.4 0.41 Y 2 0.6 0.58 Not as great of a difference between frequencies due to a low number of migrants (6) moving from P#1 t
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