Genetics & Natural Selection 2

Genetics & Natural Selection 2 - Genetics and...

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Unformatted text preview: Genetics and Natural Selection Darwin did not have an understanding of the mechanisms of inheritance and thus did not understand how natural selection would alter the patterns of inheritance in a population. It took an understanding of genetics and an understanding of evolution to merge the two fields into the cornerstone of modern evolutionary theory The Genetical Theory of Natural Selection Sir Ronald Fisher was the first to begin to develop this theory. Points to keep in mind: Natural Selection Evolution For natural selection to produce evolution selected traits must be heritable Natural selection can not increase or decrease the frequency of a trait in a population unless the trait influences reproductive success. Modes of selection: Selection can go on at different stages in the life cycle Fitness can be defined for a single genotype as the average contribution of individuals of that genotype to the population after one or more generations. Relative fitness - W the average contribution of individuals of a given genotype to the population relative to the fitness of the genotype with the highest fitness. Coefficient of selection s the amount fitness of a genotype is reduced relative to the genotype with the highest fitness. The rate of genetic change in a population depends on the relative fitness of genotypes. The mathematics of a selection model For simplicity assume that selection acts through differences in viability and otherwise the population satisfies all of the Hardy- Weinberg conditions (large population size, random mating, etc.) For a single gene with two alleles (A,a) there are three genotypes AA, Aa, and aa. Each genotype has a fitness W (WAA, WAa, and Waa). Fitness is the relative probability of successful survival and reproduction. Fitness will have a value between 0 and 1. If a genotype has a fitness of 1 this means that genotype has the highest relative fitness. A fitness of 0 means that genotype has no chance of survival to reproduction. A fitness of 0.5 means that genotype A fitness of 0....
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Genetics & Natural Selection 2 - Genetics and...

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