BIOL 202 Lecture Notes - Lecture 14: Negative Frequency, Selective Sweep, Balancing Selection

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Natural selection acting on a gene involved in pigmentation in moths. Light colours used to be prevalent, when the trees had a light colour. Industrial revolution caused the surfaces to be darkened, and the light colours used to defend against the birds are no longer useful. Fitness and natural selection: fitness is determined by the joint effects of genetic make-up and environment. Absolute fitness is then expressed by the number of offspring that survive to mate again. Relative fitness is the ratio between the genotype and the most fit genotype. Selection coefficient is s, a reduction in relative fitness. S = 0. 25 for the example used in class. (6 to 8). To calculate genotypes post selection, use the frequency of genotypes at fertilization multiplied by the fitness, divided by the average fitness. Repeating this process for several generation would then decrease the genotype frequency of unfavourable and unfit alleles. Works by negative frequency selection, whereby rare genotypes are favoured.

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