Genetic Variation in Populations

For example, individuals may carry different versions of DNA associated with inherited characteristics. Each individual has only some of the genetic variants present in the wider population, so looking across the whole population reveals much more variation than looking at one organism alone.

“Extensive” does not mean that every individual is completely different or that every visible characteristic must vary. It means that, across the population’s DNA, there are usually many genetic differences.

Mutations are the source of new genetic variants

DNA is copied when cells divide. A mutation is a change in genetic material, and mutations often arise naturally through errors during DNA copying. Some substances and radiation can also cause mutations.

When a mutation changes the DNA sequence, it creates a new genetic variant. If that variant is passed to offspring, it can enter the population. Further mutations arising over many generations introduce further variants, helping to produce the extensive genetic variation found within a species.

Sexual reproduction can place existing variants into new combinations in offspring. However, mutation is the process that creates new variants of DNA in the first place.

Variation belongs to populations

A mutation first occurs in the DNA of a particular cell, not simultaneously throughout a species. When heritable variants are passed between generations, different individuals may inherit different variants. The result is a population containing a range of genetic information rather than one identical genome shared by every member.

This variation supplies the inherited differences on which natural selection can act, although natural selection itself is a separate process. Mutations occur naturally and continuously; they do not appear because an organism needs a particular characteristic.