Dominant allele

A dominant allele is the form of a Mendelian factor that supersedes the recessive allele and completely determines the organism's phenotype. If for a given factor the dominant allele is represented by A and the recessive allele is represented by a, then Aa individuals will have the same phenotype as AA individuals.

The figure below illustrates the inheritance of an autosomal dominant disorder (i.e., a single-gene disorder inherited by a dominant allele on a non-sex chromosome). Such a disorder will be inherited independently of gender and is inherited by all organisms who possess the allele, meaning that there are no carriers for the condition (an example is Huntington's disease).

Dominant gene in autosome