What is an allele?

An allele is one of two or more versions of the same gene at the same locus on homologous chromosomes.

• Every person inherits two alleles per gene one from each parent.
• Dominant: Expressed even when one copy present (e.g., brown eyes B)
• Recessive: Expressed only when two copies present (e.g., blue eyes b)

• Homozygous: BB or bb; Heterozygous: Bb

Summary: An allele is a variant form of a gene; inherited in pairs from each parent, they determine the traits expressed in an organism.