Biology 1002B Lecture Notes - Lecture 9: Melanocortin 1 Receptor, Red-Tailed Hawk, Rela

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Shifts a trait from the existing mean and toward the favoured extreme. After selection, the traits mean value is higher or lower than before depending in the direction of selection. Predatory fish promote directional selection for larger body size in guppies when. Stabilizing selection: when individuals expressing intermediate phenotypes have the highest relative fitness. By eliminating phenotypic extremes, stabilizing selection reduces genotypic and phenotypic variation and increases the frequency of intermediate phenotypes. Most common mode of natural selection ex. Intermediate mass newborns more likely to survive than those that weight too much or too little. Alleles producing extreme phenotypes becomes more common, promoting polymorphism. Much less common than directional and stabilizing selection. Decreases the frequency of the mean phenotype but increases the frequencies of both extremes of the distribution. After selection has occurred, mean tail length may be unchanged, but the variability in ail length among individuals has increased.

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