Question

Natural populations of most species are genetically diverse. what are some of the reasons that natural polymorphisms have not become fixed for the most favorable allele at each locus ?

Answer 1

Natural polymorphisms have not become fixed for the most favorable allele at each locus because of genetic drift and Natural selection. In the case of genetic drift, an allele can be lost over time by random chance. When an allele drifts to fixation, the other allele at the same locus is lost, resulting in a loss in genetic diversity. Also, Variation in the populations gene pool allows natural selection to act upon traits that allow the population to adapt to changing environments. Sometimes, Selection also occurs against a trait with changing environment, resulting in a decrease in genetic diversity (if a disadvantageous allele is selected against). Hence natural polymorphisms have not become fixed for the most favorable allele.