Fixed allele

rdf:langString Fixed allele

rdf:langString 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. There are only two ways in which a fixed allele can become un-fixed. This can happen through random mutations that lead to the development of a new allele. Or this can happen through immigration. Fixed alleles were first defined by Motoo Kimura in 1962. He discussed how fixed alleles could arise within populations, and was the first to generalize the topic. He credits the works of Haldane in 1927 and Fisher in 1922 as being important in providing foundational information that allowed him to come to his conclusion. Kimura's later works were pivotal in the foundation of evolutionary and population genetics. Kimura is responsible for the development of the neutral theory of molecular evolution, which discusses how most of the variation and evolution within species is caused by the random fluctuation of neutral allele frequencies, so by genetic drift, rather than natural selection. More recent studies have confirmed the works of these early evolutionary biologists, showing that rates of extinction decrease with increasing beneficial alleles, that extinction of deleterious alleles occurs faster than that of beneficial alleles, and that the process of adaptation can become very complex. To illustrate what a fixed allele, imagine a population of rabbits where there are three alleles for fur color brown, gray or white. In this initial population, there is no fixed allele. Then an event, such as a forest fire, causes the elimination of one of the alleles from the population. Assume all the gray rabbits were killed in a forest fire, and now all that remains in the population are the white and brown alleles. This happens in the summer, so there is no snow, and the white rabbits fall prey to owls more often than brown rabbits. Eventually the only remaining allele in the population is the brown allele, this allele is now a fixed allele. Fixed alleles are a very important aspect of evolutionary biology. Low genetic diversity, which is seen with allele fixation, is dangerous as it can lead to mass extinctions. If there is little genetic variability within a population and the genetically similar individuals all are susceptible to a certain pathogen, the population will likely cease to exist. This is why there are examples of populations with fixed alleles becoming threatened or endangered. A great example of why fixed alleles matter is the US agriculture supply and the threat of bioterrorism. Many crops grown in the US are genetically similar, and allows for the possibility of devastating bioterrorism. Should a pathogen be developed targets certain crop supplies, such as corn, which are pivotal to the US food supply and therefore vital to the US's economic state, disastrous events could occur as the food supply could be depleted very quickly.