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The word "allele" is a short form of "allelomorph" ("other form", a word coined by British geneticists William Bateson and Edith Rebecca Saunders) in the 1900s, [7] [8] which was used in the early days of genetics to describe variant forms of a gene detected in different phenotypes and identified to cause the differences between them.
The allele frequency is distinct from the genotype frequency, although they are related, and allele frequencies can be calculated from genotype frequencies. [ 1 ] In population genetics , allele frequencies are used to describe the amount of variation at a particular locus or across multiple loci.
(For example, Df(E1)/Df(GN50) in Stowers, et al. 2000 [3]). By way of example, transheterozygote (heteroallelic combination) can result from a cross between two organisms with genotypes AA* and AA', where A is the wild type allele
The allele frequency spectrum can be written as the vector = (,,,,), where is the number of observed sites with derived allele frequency .In this example, the observed allele frequency spectrum is (,,,,), due to four instances of a single observed derived allele at a particular SNP loci, two instances of two derived alleles, and so on.
Fitness is often defined as a propensity or probability, rather than the actual number of offspring. For example, according to Maynard Smith, "Fitness is a property, not of an individual, but of a class of individuals—for example homozygous for allele A at a particular locus.
An allele is said to be dominant if it is always expressed in the appearance of an organism (phenotype) provided that at least one copy of it is present. For example, in peas the allele for green pods, G, is dominant to that for yellow pods, g. Thus pea plants with the pair of alleles either GG (homozygote) or Gg (heterozygote) will have green ...
The expressed allele is dependent upon its parental origin. For example, the gene encoding insulin-like growth factor 2 (IGF2/Igf2) is only expressed from the allele inherited from the male. Although imprinting accounts for a small proportion of mammalian genes, they play an important role in embryogenesis particularly in the formation of ...
An example in dog coat genetics is the homozygosity with the allele "e e" on the Extension-locus making it impossible to produce any other pigment than pheomelanin. Although the allele "e" is a recessive allele on the extension-locus itself, the presence of two copies leverages the dominance of other coat colour genes.