Lecture23_slides_21Oct2011 - 10/10/2011...

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10/10/2011 1 Genetic change may occur through: Natural Selection Genetic Drift • Migration Mutation A genetic definition of evolution: Evolution is any genetic change in a population. Migration can introduce new alleles into populations, and can change the frequency of existing alleles. A A A A A A A A A A A A A A A A A a A a A a A a A a A a A a A a a a A a a a a a a a a a a a freq(a) = 22/40 Migration as an evolutionary force. a Population 1 freq(a) = 0/7 freq(a) = 2/9 freq(a) = 20/38 Population 2 Migration can introduce new alleles into populations, and can change the frequency of existing alleles. A A A A A A A A A A A A A A A A A a A a A a A a A a A a A a A a a a A a a a a a a a a a a a Migration as an evolutionary force. a Population 1 Population 2 After migration, a fraction m of the population consists of Immigrants. (1 – m) are previous residents. Gene Flow: The movement and incorporation of genes from one population into the gene pool of another population. By “migration” we mean gene flow: Migration this means more that just movement of individuals, the migrants must have reproductive success!! 1. Individuals may migrate to new locations and found new subpopulations. 2. Existing populations may become fragmented by newly arising barriers. 3. Distant points in a species range may be isolated from each other by virtue of physical (geographic) distance. In order for migration to be genetically meaningful, populations need to subdivided. How do populations become subdivided?
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10/10/2011 2 Founder effects parent population founded population A small population is founded by just a few individuals. Allele frequencies in the founded population will be different from “parent” population because of sampling error (just like genetic drift in small populations).
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Lecture23_slides_21Oct2011 - 10/10/2011...

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