Allele frequency

relative frequency of a variant of a gene at a particular locus in a population

Allele frequency refers to the different forms of a gene at a single position on a chromosome. It is the proportion of a given allele to all alleles at the same locus.[1][2] It is usually expressed as a percentage.

Allele frequencies may be used to describe genetic diversity in a population. If the frequency of any allele is above 1% it is probable that natural selection is maintaining it at this level. This is because the natural mutation rate of an allele is almost always much lower than 1%.

A fixed allele is one allele that exists for a particular population. A fixed allele is homozygous for all members of the population.[3]

The term allele refers to one variant gene out of several possible for a particular locus in the DNA. When all but one allele go away, one only remains. That allele is said to be fixed.


  1. King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p16
  2. Klug W.S; Cummings M.R; Spencer C.A. & Palladino M.A. Concepts of Genetics. 10th ed, Pearson. p700–706, including worked examples.
  3. "fixed allele definition".