Allele frequency

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