∞ generated and posted on 2016.08.18 ∞
Variety of a gene, particularly as found at a single locus.
| Genes often vary from individual to individual within a species and the different varieties that individual genes come in are called alleles; this is equivalent to saying that strawberry (allele) is a kind of ice cream (gene), as too are chocolate (allele) and vanilla (allele). |
Allelic versions of the same gene tend to be subtly differ from each other, differing for example by only one or a few bases of hundreds or thousands of bases. Only a single type of allele can exist at a specific locus on a specific chromosome. Different chromosomes of the same type, however, can possess different alleles, that is, different versions of the same gene at the same locus.
In terms of its impact on fitness, an allele can be described as neutral, detrimental, lethal, or even beneficial. It is important to keep in mind, however, that these designations are not invariant for a given allele but instead are dependent on the environment an organism finds itself in as well as what other alleles are found within the same organism, i.e., making up its genotype.
Haploid can posses only a single allele at each locus. A diploid individual contains two alleles at each locus (at least for autosomal chromosomes). A individual possesses up to three alleles of each type, etc.
Note that for these latter individuals those multiple alleles can be either identical (homozygosity), different (heterozygosity, especially as considered in the diploid case), or any permutation of combinations with the only limitation being the number of examples of a given locus that are found within a single individual and the number of alleles found at that locus which are present within the larger population.
In order for evolution to act at a given locus, a population must possess more than one allele at that locus. The existence of more than one allele at a given locus, within a population, represents genetic variation, otherwise known as a .
Video (Nice overview of the importance of genetic variation as considered in terms of )
Video (Basic discussion of what are all about, their underlying alleles, and the genetics of )