Biology 1001A Lecture Notes - Lecture 14: Genotype Frequency, Allele Frequency, Stabilizing Selection
19 Feb 2016
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Document Summary
Pre-lecture: examples of directional, stabilizing, and disruptive selection, directional selection relative fitness. When individuals near one end of the spectrum have the highest. Directional selection shifts a trait away from the existing mean and towards the favoured extreme. Most cases are of artificial directional selection and they are aimed at increasing or decreasing specific phenotypes: disruptive selection phenotypes, stabilizing selection. When individuals expressing intermediate phenotypes have the highest relative fitness. By eliminating extreme phenotypes, stabilizing selection reduces genetic/phenotypic variation and increases frequency of intermediate phenotypes. Opposing directional selection can sometimes produce stabilizing selection. Extreme phenotypes have higher relative fitness over intermediate. Alleles producing extreme phenotypes become more common, promoting polymorphisms. Less common than directional or stabilizing selection. Mean phenotype unchanged, but variability of phenotypes increases: how inbreeding and nonrandom mating affect allele frequencies, and how they affect genotype frequencies, inbreeding: genetically related individuals mate with each other. Organisms living in small, closed-off populations tend to mate with related individuals.
