One of two or more alternate forms of a gene or marker at a particular locus on a chromosome.

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).

Dr. Leslie Biesecker, of the National Human Genome Research Institute's Laboratory of Genetic Disease Research, defines allele.
related terms: chromosome, deletion, deoxyribonucleic acid (DNA), dominant, gene, insertion, locus, recessive, substitution.