What is Allele?
An '''allele''' is a form of a [[gene]] at a particular position ('''locus''') on a [[chromosome]].<ref name=dict>King R.C. Stansfield W.D. & Mulligan P.K. 2006. ''A dictionary of genetics'', 7th ed. Oxford.</ref><sup>15</sup> It is the bit of coding [[DNA]] at that place.<ref name=popgen>Gillespie, John H. 2004. ''Population genetics: a concise guide'', 2nd ed. Johns Hopkins University Press, Baltimore.</ref><sup>p6</sup> Typical plants and animals have two sets of chromosomes, one set inherited from each parent.<ref name=dict/><sup>123</sup> These organisms are called [[diploid]]. Since such organisms have two sets of chromosomes, they have (except on the [[sex chromosome]]s) two alleles at each gene '''locus'''.<ref name=popgen/><sup>p6</sup> If the two alleles are identical, the individual is called a '''homozygote''' and is said to be '''homozygous'''. If instead the two alleles are different, the individual is a '''heterozygote''' and is '''heterozygous'''.<ref name=dict/><sup>205</sup> == Dominance == In a heterozygote the effect of one allele may completely ‘mask’ the other. That is, the [[phenotype]] produced by the two alleles in heterozygous combination is identical to that produced by one of the two homozygous genotypes.<ref name=dict/><sup>212</sup> The allele that masks the other is said to be '''dominant''' to the latter, and the alternative allele is said to be '''recessive''' to the former. This idea originates in the work of [[Gregor Mendel]], the founder of [[genetics]]. In other cases, both alleles contribute to the phenotype. === Example === The inheritance of alleles, and their dominance, can be represented in a [[Genetics#Punnett squares|Punnett square]]. An example is the gene for blossom colour in many species of [[flower]]. A single gene controls the colour of the [[petal]]s, but there may be several different versions (or alleles) of the gene. In this example, parents have the genotype '''Bb''' (capital letters show dominant alleles and lower-case letters to show recessive alle