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