ABSTRACT
A population in Hardy-Weinberg equilibrium may be compared to a ball placed on a horizontal surface – like a pool table. When the fitness of heterozygotes is lower than that of both homozygotes, a partial reproductive barrier is formed that may lead to the separation of two gene pools. When the hybrids between two genotypes have a phenotypic physiological or reproductive advantage over the parents, the phenomenon is described as hybrid vigor. The American population geneticist, Sewall Wright, suggested a graphic illustration of the effects of natural selection on fitness. The ‘genetic landscape’ is portrayed as a topographical map. At allele frequencies lower than the equilibrium point, selection will increase the frequency of a. At frequencies above the equilibrium, selection will decrease the frequency of a – in both cases selection will invariably increase average fitness. The American population geneticist, Sewall Wright, suggested a graphic illustration of the effects of natural selection on fitness.
