the inheritance of a single trait, a trait that may be controlled by one, a few, or many genes. The goal of population genetics is different. Rather than studying the inheritance of a trait, population genetics attempts to describe how the frequency of the alleles which control the trait change over time. To study frequency changes, we analyze populations rather than individuals. Furthermore, because changes in gene frequencies are at the heart of evolution and speciation, population and evolutionary genetics are often studied together.
For a population of individuals to succeed over evolutionary time, it must contain genetic variability. Because we do not know all the genetic variables that would predict evolutionary success, we study the variability of different phenotypes and genotypes to provide an overview of the population. The traits that are analyzed can be outward phenotypes that can be easily scored. More recently, biochemical and RFLP data has been used to assess population variability.
This image illustrates a key concern of population genetics --- the measurement of variability. This is a collection of snail shells. As you can see, many different patterns and colors are possible for the shells. Clearly many different alleles exist that control color and shape. This is an example of a polymorphic or variabile population.