AP BIOLOGY

Detailed explanation-1: -The directional selection theory says that an extreme phenotype (characteristics or traits) is favored over other phenotypes and this causes the allele frequency (how often the variant of a gene shows up in a population) to shift over time in favor of the extreme phenotype.

Detailed explanation-2: -Directional selection occurs when individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other. It has been demonstrated many times in natural populations, using both observational and experimental approaches.

Detailed explanation-3: -Directional selection effects the concentration of increasing alleles for the behavioral trait in question in the line selected in the upward direction and of decreasing alleles in the one selected in the downward direction.

Detailed explanation-4: -Under directional selection, relative fitness increases as the value of a trait increases (positive directional selection) or decreases (negative directional selection).