genetic dominancemedical dictionary

Denoting a pattern of inheritance of an autosomal mendelian trait due to a gene that always manifests itself phenotypically; generally, the phenotype in the homozygote is more severe than in the heterozygote, but details depend on what criterion of phenotyping is used.

Dominance of traits, an expression of the apparent physiologic relationship existing between two or more genes that may occupy the same chromosomal locus (alleles). at a specific locus there are three possible combinations of two allelic genes, A and a: two homozygous (AA and aa) and one heterozygous (Aa). If a heterozygous individual presents only the hereditary characteristic determined by gene A, but not a, A is said to be dominant and a recessive; in this case, AA and Aa, although genotypically distinct, should be phenotypically indistinguishable. If AA, Aa, and aa are distinguishable, each from the others, A and a are codominant.

(05 Mar 2000)