Question

125) Directional selection generates a phenotypic shift A) toward an extreme of the phenotype B) away from either extreme of the phenotype C) toward both extremes of the phenotype D) toward the mean of the extremes of the phenotype

Answer 1

Natural selection is major source of evolution through which characteristics (heritable traits) of a population changes/evolve over a period and new species is generated (survival of the fittest in the environment). Directional selection is a one of the types of natural selection in which extreme phenotype is favored over the all other phenotypes present in the population, and leads to shift in the direction of the allele frequency of the favored extreme phenotype. As a result over a period , the population consist of with organisms having favored extreme phenotype. Therefore, option "A" toward an extreme of phenotype is the right answer.

Directional selection favors one of the extreme phenotypes in population and causes phenotypic shift toward that phenotype. This type of selection does not generate a population which is not having one of the extreme phenotype. Therefore, option "B" away from either of the phenotype is not the right answer.

A natural selection which favors both extremes of the phenotype is known as disruptive selection, therefore option "C" toward both extremes of the phenotype is not the correct answer.

A natural selection which favored intermediate phenotype over the extreme phenotypes in a population is known as stabilizing selection. Therfore, option "D" toward the mean of the extremes of the phenotype is not the right answer.