Compare and contrast directional selection and disruptive selection and provide an example of each.

Directional selection and disruptive (or
diversifying) selection are two types of natural selection. There is another type of natural
selection: stabilizing selection.

Directional selection favors an extreme
phenotype (that is, a trait or characteristic of a species). This results in an increase in the
population of organisms that display the extreme phenotype as compared to other members of the
same species. For example, in a mice population on a beach, fur color may provide camouflage
from predators. The mice whose fur color is closest to that of the sand will survive, while
other mice will fall prey to predators. This will ensure the survival of mice with a particular
fur color.

Disruptive selection also favors extreme phenotypes; however,
unlike directional selection, this type of selection favors two extremes. For example, in the
same scenario with the mice, disruptive selection might emerge if there are tall, dark trees in
addition to sand. In that case, the mice with a darker fur color will also have a higher
survival rate. Thus, both light- and dark-colored mice will survive.

Neither
of these selections results in a decrease in the genetic variance of the given
population.

Both of these selection types do not favor the average or
middle-of-the-road phenotype. This is where stabilizing selection, the most common type of
natural selection, comes in.

Hope this helps.