An allele is one of a pair of genes that appear at a particular location on a particular chromosome and control the same characteristic, such as blood type or color blindness. Alleles are also called alleleomorphs.

Your blood type is determined by the alleles you inherited from your parents. If your mother's blood type is A and you know she's homozygous (that is, her alleles are the same, both of them A) and your father's blood type is O (since type O is a recessive trait, he would have to be homozygous, too), then you’ve inherited an A and an O allele — and your blood type is A.

Definitions of allele

n (genetics) either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a particular chromosome and that control the same character

“some alleles are dominant over others”
dominant, dominant allele
an allele that produces the same phenotype whether its paired allele is identical or different
recessive, recessive allele
an allele that produces its characteristic phenotype only when its paired allele is identical
Type of:
cistron, factor, gene
(genetics) a segment of DNA that is involved in producing a polypeptide chain; it can include regions preceding and following the coding DNA as well as introns between the exons; it is considered a unit of heredity

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