BIOL 2P05 Lecture Notes - Lecture 12: Allele Frequency, Directional Selection, Point Mutation
6 Feb 2018
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Document Summary
Dark mice have the same fitness in each environment (independent) of how rare or common their colour is. One allele is consistently favoured over the other --> pocket mouse example. Selection drives allele frequencies in a single direction. Eventually favoured allele will become fixed in the population. Rates of fixation under directional selection if there is dominance of incomplete dominance. A1a2 heterozygote has a higher fitness than either of the homozygotes. The direction of natural selection depend on the current allele frequencies in the population -> eventually reaches an intermediate frequency. Which allele gets fixed depends on starting frequencies. If a1 starts with lower frequency, it is lost from the population. Base pair mutation that turns glutamate into valine. A recessive blood disorder caused by point mutation in hemoglobin gene. A2a2 = hh = sickele shape --> low fitness. When malaria is not present - homozygous dominant advantage. Two or more alleles are maintained in the population.
