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9 Mutation - p = μ s where μ is the mutation rate and s...

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BIO 370 Kirkpatrick & Hall, Fall 2004 p. 1 9. Mutation Mutation plays two roles in evolution It is the ultimate source of all new genetic variation It changes the frequencies of alleles that already exist in a population Most new mutations are deleterious (they decrease fitness) Data for typical new mutations in Drosophila When heterozygous, they reduce fitness by 3% When homozygous, they reduce fitness by 10% This is easy to understand: most random changes to an amino acid sequences will make an enzyme less efficient (Of course, some new mutations are advantageous) Any particular locus will reach a mutation-selection equilibrium Here the number of new mutations coming into the population is balanced by the number being removed by selection The frequency of the deleterious mutation is then:
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Unformatted text preview: p = μ / s where μ is the mutation rate and s is the fitness disadvantage of the mutant heterozygote Example: with μ = 10-5 and s = 0.03, the equilibrium frequency of the deleterious mutation is 10-5 / 0.03 = 3 x 10-4 Even though the frequency of a deleterious mutation at one locus is typically small, there are a lot of loci in the typical genome We each carry many deleterious mutations Most are ones our parents also have and they passed down to us But we also have some new ones that appeared in the egg and sperm that we came from We may each have on average one new deleterious mutation Deleterious mutations are important to human health They cause genetic diseases (diabetes, cancers, coronary problems, . ..) They are an important cause of aging...
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