One of the alternative versions of a gene at a given location (locus) along a chromosome
Definition from: GeneTests
from the University of Washington and Children's Health System, Seattle
One of the variant forms of a gene at a particular locus, or location, on a chromosome. Different alleles produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one).