Fixed allele

A fixed allele is an allele that is the only variant that exists for that gene in all the population. A fixed allele is homozygous for all members of the population. The term allele normally refers to one variant gene out of several possible for a particular locus in the DNA. When all but one allele go extinct and only one remains, that allele is said to be fixed.Fixation is the process through which an allele becomes a fixed allele within a population. There are many ways for an allele to become fixed, but most often it is through the action of multiple processes working together. The key driving force behind fixation is natural selection and genetic drift. Natural selection was postulated by Darwin and encompasses many processes that lead to the differential survival of organisms due to genetic or phenotypic differences. Genetic drift is the process by which allele frequencies fluctuate within populations. Natural selection and genetic drift propel evolution forward, and through evolution alleles can become fixed.One example of a fixed allele is the DGAT-1 exon 8 in Anatolian buffalo. A non-conservative mutation in the DGAT-1 allele, which produces a protein with a lysine at position 232 instead of an alanine. This mutation produces a protein different from the wild type protein. This mutation in cattle has an effect in milk production. Investigation into three water buffalo populations revealed four different haplotypes each having a single nucleotide polymorphism (SNP), however all of these SNPs were conservative mutations, causing no change in protein production. All populations of Anatolian buffalo studied had the non-conservative lysine mutation at 232, leading to the conclusion that this DGAT-1 allele mutation is fixed within the populations.