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Synthesis Notes

Balanced polymorphisms overdominance and negative

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Unformatted text preview: cess where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population.  in positive (or purifying) frequency ­dependent selection, the fitness of a phenotype increases as it becomes more common.. similar to underdominance. Example: snail shells/chirality, aposematism  In negative (or diversifying) frequency ­dependent selection, the fitness of a phenotype increases as it becomes rarer. This is an example of balancing selection. As frequency of allele goes up, the fitness goes down. overdominance 12 How do the different types of selection affect variation in a population? All answered above What are balanced polymorphisms and unstable equilibria?  ­ Balanced polymorphisms ­ a stable equilibrium in which more than one allele is present at a locus  ­ Unstable equilibria ­ gets rid of polymorphisms and pushes to the extremes What types of selection produce them?  ­ Balanced polymorphisms ­ overdominance and negative frequency dependent selection  ­ Unstable equilibria ­ underdominance What two roles does mutation play in evolution?  ­ Creates variation  ­ Alters allele frequencies  ­ In a qualitative (i.e., non ­numeric) way, how does changing the mutation rate or the strength of selection affect mutation ­selection balance? ??????????  ­ Mutation selection balance: an equilibrium frequency of deleterious mutations in which these deleterious mutations are maintained at a positive frequency in a population due to a balance between ongoing deleterious mutation and the purging effect of natural selection  ­ Ummm… help?  ­ If mutation rates are equal: The mutation rates would be ½. If the mutation rates from A1 to...
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