Population Notes

# Population Notes - 1 Population Genetics We have defined...

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We have defined evolution as change in a population over time. A more precise definition, that takes into account the genetic basis of the change, is the following: Evolution is the change in allele frequencies and/or genotypic frequencies in a population over time. This change is measured by population genetics , first described mathematically by Hardy and Weinberg. Population genetics, unlike Mendelian genetics, describes the kinds of offspring a typical couple from a population would have. This, in turn, depends on the genetic make-up of the population , rather than on the specific genotypes of a particular couple, and is based entirely on probability. For a typical mating couple from a given population, their chance of producing gametes with a given allele depends on that allele’s frequency in the population. For example, if polydactyly (which codes for extra digits on hands and/or feet) is a rare allele, the couple’s chance of making a gamete carrying the polydactyly allele is low. We can compare the chance of particular gametes’ being made by individuals in a population with the chance of randomly picking white or black socks from a bag containing a “population” of 100 black and white socks. If there are equal numbers of black and white socks in the bag, the chance of being picked = 0.5 (50%) for each color. If there are 90 white socks and 10 black socks, the chance = 0.9 (90%) for a white sock, and 0.1 (10%) for black. 1

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Population Notes - 1 Population Genetics We have defined...

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