7) Drift outline.docx - BIO 370 Mark Kirkpatrick Instructor p Random genetic drift Reading in F&K Chap 7 Simulation 3 clam pops Atlantic Pacific and

7) Drift outline.docx - BIO 370 Mark Kirkpatrick Instructor...

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BIO 370 Mark Kirkpatrick, Instructor p. ° Random genetic drift Reading in F&K : Chap 7 Simulation: 3 clam pops: Atlantic, Pacific and Indian Ocean. Each pop has 2 clams and a sea goddess. There are 2 alleles that don’t affect fitness (black and red) and each clam has 2 of these. All clams start as homozygotes. o Zygotes mature into adults, all individuals survive and there’s no selection o Adults then make 5 gametes from each allele (5 red, 5 black) and release them into ocean. Adults then die. o Next generation begins w/ zygotes formed by random fertilization. Generation 1 Generation 2 Generation 3 Generation 4 Atlantic 1/2 1/2 3/4 1/2 Pacific 1/2 1/2 1/4 1/4 Indian 1/2 1/2 1/2 0 o Results: Was there evolution? Yes, there was evo b/c there was an inherited change in a gp of organisms across generations. Was there natural selection? No b/c the allele frequencies changes randomly and not based on survivability When did the allele frequencies change? Not during gametogenesis: 5 and 5 for each allele during meiosis. Not during adult’s time Allele frequency changed during fertilization b/c of random sampling of alleles to start the next gen. Why did allele freq change? Inheritance is always a random process. When anyone goes to make a gamete, meiosis flips a coin as to what copies of a gene are passed on in that gamete- one will not be passed on. They change b/c of random chance! Random genetic drift: Changes in allele frequencies caused by the random sampling of genes o From chance events of survival, repro (hetero at a locus for two alleles, only one is passed) and inheritance. Genotype and phenotype aren’t the only factors that determine if they leave genes to the next generation (selection) The principle was not known to Darwin, but was worked out by Sewell Wright and others in the 20 th century o Known for mathematic analysis of genetic drift and the University of Chicago w/ guinea pigs.
BIO 370 Mark Kirkpatrick, Instructor p. ° Key points: Drift causes evolutionary change in the absence of selection 1. Drift is unbiased. An allele frequency is as likely to go up as to go down. Natural selection can favor one allele over another b/c of survival and repro, but genetic drift doesn’t. o Allele frequencies are equally likely to go up or down – no systematic trend 2. Genetic variation within each population is eventually lost (one allele or the other will become fixed) o Random genetic drift causes genetic variation to be lost Results of drift within a populations: sometimes allele frequencies go up or down and overtime it will go to 100% or 0%. Once this happens, no genetic variation.

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