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Biology 3300- Genetic Drift

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University of Lethbridge
BIOL 3300
Theresa Burg

Biology 3300 Jan.29th Midterm next Friday- material up to and including this Friday’s class Genetic drift is random Allele frequencies in population change from generation to generation due to chance A1= 0.6 A1A1= 6 A1= (6+6+2)/(2*10) = 14/20 = 0.7 A2= 0.4 Random union of gametes A1A2= 2 A2= (2+2+2)/(2*10) = 6/20 = 0.3 n= 10 A2A2= 2 Drift can act on gametes or individuals - Cannot produce adaptation, can lead to fixation of alleles - Drift doesn’t introduce or produce alleles, migration does introduce new alleles - Also introduce new alleles through mutation - Small population sizes can lead to fixation As sample size increases, sampling error decreases - A1 starting frequency 0.6 - Over time the cumulative frequency should level out Causes of Genetic Drift - Population bottlenecks: events that randomly remove most members of the population - Founder effects: process that randomly disperse a small number of individuals to a new location. These individuals form the new population o Individual that colonize new habitat o Starting new population o Differences are quite dramatic Migration: moving between existing populations - Increases population variation - Decreases differences among population Genetic drift: starting a new population - Decreases population variation - Increases differences among population - Have potential to lose alleles Ex: Silver-eyes - Found in southern hemisphere - Have 5 subspecies (represented as circles on map) - Based on history they know when they move between different areas - Have a series of founder events - Every time they moved up there were bottleneck populations occurring - Can see significant variation of wing length between the subspecies - Within the one subspecies there are differences in wing length (white circles show differences by 3mm) - Found that the last island colonized (Norfolk) has 60% of allelic diversity found in Tasmania (the first island) - By the time you get to the end there is a significant difference between genetic diversity present Drift: - Effects are stronger and occur faster in small populations - Over time drift leads to large changes in allele frequencies - Because fluctuations are random, o Each population has unique evolutionary trajectory  What happens in one population won’t impact another population o
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