Allele (source code)
= Allele
{wiki}
An <allele> is one of the alternative inherited states at a <genetic locus>, often distinguished by a difference in <DNA> sequence. A population can contain many <alleles>, although a two-copy <diploid> individual carries at most two at that <genetic locus>, one inherited from each parent. See https://www.genome.gov/genetics-glossary/Allele[NHGRI: allele].
Count copies, not just individuals, when computing <allele frequency>: in 100 individuals with <genotype> counts $49\ AA$, $42\ Aa$, $9\ aa$, there are $2(49)+42=140$ copies of $A$ among 200, so $p_A=0.70$. The <heterozygotes> contribute to both <allele> counts. This converts observed <genotypes> into the population quantity needed by the <Hardy-Weinberg principle>.
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