Allele

An allele is any one of a number of viable DNA codings of the same gene (sometimes the term refers to a non-gene sequence) occupying a given locus (position) on a chromosome. An example is the gene for blossom color in many species of flower - a single gene controls the color of the petals, but there may be several different versions of the gene. One version might result in red petals, while another might result in white petals.

Equations

There are two simple equations to look at the frequency of an allele (see Hardy-Weinberg principle):

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Equation 1: p^2+2pq+q^2=1

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Equation 2: p+q=1

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Where p is the frequency of the dominant gene, q is the frequency of the recessive gene. p2 is the number of species that are homozygous dominant for a trait, pq is the number that are heterozygotes and q2 is the number that are homozygous recessive. Natural selection can act on the aforementioned components to equation one, and obviously affect the frequency of genes seen in equation 2.

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