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Unformatted text preview: 10/1 /2011 1 You study finches on a tiny island. These finches have genetic variation for beak size, and larger-beaked birds can crack harder seeds. A tsunami kills most of the birds on your island. By chance, a greater proportion of the birds that escaped the storm had small beaks. Before the tsunami, mean beak depth was 15.2 mm. After the tsunami, mean beak depth in the population had decreased to 12.7 mm. iClicker question to start lecture! (hooray!) A) The finch population did not evolve. B S ll b k d ti d i th t i B) Smaller beaks were adaptive during the tsunami, so the finches evolved in response to natural selection. C) The finch population evolved, but natural selection had nothing to do with it. D) Having the first slide be a Clicker is unfair to students who are late for class. E) I can’t answer because *I* am late for class. Genetic change may occur through: • Natural Selection • Genetic Drift A genetic definition of evolution: Evolution is any genetic change in a population. • Migration Mutation Allele frequencies: freq( A red ) = 0.58 freq( A yellow ) = 0.42 Allele frequencies in survivors: freq( A red ) = 0.61 freq( A yellow ) = 0.39 Allele frequencies: freq( A red ) = 0.58 freq( A yellow ) = 0.42 PRE- Genetic Drift 10/1 4 /2011 2 Allele frequencies in survivors: freq( A red ) = 0.61 freq( A yellow ) = 0.39 POST- Genetic Drift Random Genetic Drift • Real populations are finite in size. • Random sampling of gametes and/or adults can change allele frequencies in populations. • This is evolution (even though it is not adaptive). Assumptions underlying Hardy-Weinberg Equilibrium • No mutation • No selection • No migration • Infinite population size (no genetic drift) • Random mating We assume: There are no chance events that change allele/genotype frequencies. Allele frequencies are perfectly transmitted from one generation to the next. q p p q p 2 q 2 p q p q A a A A a A a AA A a (0.5) (0.5) (0.5) (0 5) x (0 5) = (0 5) x (0 5) = a A a A a aa A a (0.5) (0.5) x (0.5) = 0.25 (0.5) x (0.5) = 0.25 (0.5) x (0.5) = 0.25 (0.5) x (0.5) = 0.25 A a A a What if they only have one kid?...
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This note was uploaded on 01/01/2012 for the course BIOEE 1780 taught by Professor Harrison during the Fall '10 term at Cornell.
- Fall '10