BIOL 123 Lecture Notes - Lecture 9: Epistasis, Genetic Drift, Natural Selection

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1 Jan 2021
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Natural selection arises when (1) individuals vary in the expression of their phenotypes and (2) this variation causes some individuals to perform better than others: focus on how selection changes the frequencies of alleles in a population. Reliable proxies of fitness: can measure probability that an individual survives to the age of reproduction. Difficult to measure because of relationship between phenotype and genotype: fitness of organism is the product of its entire phenotype. To understand how selection leads to changes in frequencies of alleles, we can consider the contributions of a specific allele rather than a genotype, to fitness. Alleles can differ enormously in their effects on fitness. Over time, an allele with a slightly higher average excess for fitness can come to dominate a population. Small population = genetic drift is stronger; large population = genetic drift is weaker.

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