Which statement best explains how the effect on a particular allele can change the genetic makeup of a population over time?

Genetiic variation is simply the different variety of genetic make up and what is called alleles. Alleles are similar to a code for the body which determines such things as hair color, eye color, height, and other factors.

Genetic variation is therefore the variation between genes and alleles, within a small or large group of people. A small group of people would for example be a family. A large group of people would for example be the population of a certain geographic region such as a country.