Explain your simulation results by calculating 4Nes for each set of fitness values.

The interplay of genetic drift and natural selection can also be simulated in PopGene.S2 by selecting the Drift menu and then the Drift + Selection + Mutation model. First try parameters of 20 populations, population size of 20, initial allele frequency of 0.5, 100 generations, relative fitness values of 1, 0.95, and 0.90, and mutation rates of 0.005. Modify these parameter values to get outcomes you would expect when genetic drift is the stronger process as well as when natural selection is the stronger process.

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The nearly neutral theory predicts that the rate of substitution will depend on the effective population size for the proportion of mutations in a population that are nearly neutral (4Nes ~ 1). The nearly neutral theory therefore predicts that the amount of polymorphism in populations depends for some mutations on the effective population size. A consequence is that subdivided populations and different species can exhibit different levels of polymorphism based on their effective population size. Similarly, rates of divergence can also vary between species, due to differences in Ne. This is in contrast to the neutral theory, which predicts that the rate of substitution is independent of the effective population size.

8.2 Measures of divergence and polymorphism

• Measuring divergence of DNA sequences.

• Nucleotide substitution models correct divergence estimates for saturation.

• DNA polymorphism measured by number of segregating sites and nucleotide diversity.

Most natural and laboratory populations contain at least some, and often a large amount, of genetic variation represented by different alleles found at the many loci in the genome. The smallest possible unit of the genome is a homologous nucleotide site, or single base-pair position in the exact same genome

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