directional,stablizing, and distuptive

     Directional selection favors those individuals who have extreme variations in traits within a population. Stabilizing selection favors the norm, the common, average traits in a population .Disruptive selection, like directional selection, favors the extremes traits in a population. Disruptive selection differs in that sudden changes in the environment creates a sudden forces favoring that extreme. Directional occurs when selection favors one extreme trait value over the other extreme. This typically results in a change in the mean value of the trait under selection. Distuptive occurs when selection favors the extreme trait values over the intermediate trait values. In this case the variance increases as the population is divided into two distinct groups. Disruptive selection plays an important role in speciation. Stablizing occurs when selection favors the intermediate trait value over the extreme values. Populations under this type of selection typically experience a decrease in the amount of additive genetic variation for the trait under selection.