Quick Definition: What Is An Allele?

An allele is an alternate version of a gene within a population. Here we look at examples of exactly what that means.


According to our best current estimations, humans have roughly 20,000 genes that either code for proteins or act as templates for functional RNA chains. These gene products (proteins and functional RNAs) interact with each other and other molecules in their environment to produce your traits.

An allele is an alternate version of a specific gene. That might sound confusing so here’s an example to help make sense of it:

If you were to compare your 20,000 genes to a friend’s 20,000 genes, you would find that some of them are different due to mutations. If we suppose that gene number 213 helps determine eye color, you might have a variation of gene 213 that makes your eyes blue while your friend might have a version of gene 213 that makes her eyes brown. This means you each have different alleles (different versions) of gene number 213.

New alleles are constantly arising in populations due to mutations. Natural selection can act on alleles, promoting some over others. Allele competition is so important that some biologists define evolution as the “change in allele frequencies within a population over time“.


Our videos benefit from guidance and advice provided by experts in science and education. This animation is the result of collaboration between the following scientists, educators, and our team of creatives.

  • Joanna Masel, PhD
  • PZ Myers, PhD
  • Jon Perry
  • Anthony Danzl