Key terms

* gene pool- the stock of different genes in an inter breeding population.

* allel frequency- the number of times an allel occurs in a gene pool.

* single-gene traits - May have just two or three phenotypes

* polygenic trait- a trait that is controlled by two or more genes.

* directional selection - when individuals at the end of the curve have higher fitness than the others.

* Stabilizing selection- when individuals hear the center of the bell curve have the highest fitness.

* disruptive selection - when the average types have a harder time surviving.