The factors that cause shifts in allelic frequencies are those factors that determine evolution. What factors cause shifts in allelic frequencies; what does the Hardy-Weinberg principle state about these factors? Can the four conditions of stability named by the Hardy-Weinberg principle ever exist completely in any population? Explain how genetic drift, mutation pressure, gene flow, and selection pressure are each likely to upset these conditions of stability in a given population.
In 1908, G. H. Hardy, an Englishman, and W. Weinberg, a German, both independently recognized that shifts in allelic frequencies and, thus, evolutionary changes only occur when something disturbs the genetic equilibrium in which the gene pool ordinarily exists. The Hardy-Weinberg Principle states that allelic frequencies and genotypic ratios will remain constant from generation to generation in sexually reproducing populations if four conditions of stability hold true. First, the population must be large enough so that chance alone would be unlikely to alter allelic frequencies. In populations with more than 10,000 breeding age members, chance elimination of an allele from the gene pool is unlikely. Thus, chance plays a insignificant role in the evolutionary change of most large, stable populations. However, in small breeding populations of less than 100, chance elimination of an allele, even an allele of adaptive superiority, is very likely. Evolutionary change in small populations based on chance
