BIOB51H3 Lecture Notes - Lecture 13: Spinal Muscular Atrophy, Frequency-Dependent Selection, Neurodegeneration
20 Mar 2019
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Mm = neurodegenerative disease (fitness: 0. 1) (most severe form: mortality < 2 years) 0. 01 = freq of m" allele (caucasian population, usa) Because this look like a one allele favoured situation with the wild type would be favored over the neurodegenerative carrying recessive allele. X hypothesis 1: negative frequency dependent selection: no fluctuation in allele frequency or fitness. X hypothesis 2: heterozygote superiority: no evidence for higher fitness of heterozygote under any circumstances. Deleterious alleles may persist at equilibrium despite selection if: Rate of loss (selection) = rate of creation (mutation: under mutation selection balance, freq (deleterious allele) will not change over time (you expect it to be at equilibrium) Because mutation is creating those alleles at a rate equal to a rate at which they are being lost from the population through selection. Fitness mm = 1 sm sm = 1 fitness mm ( s being selection against them)
