For other non-genetic uses of the term "dominance", see
Dominance. In
genetics, a dominance relationship refers to how the
alleles for a
locus interact to produce a
phenotype.There are three main kinds of dominance relationships:Simple dominance or complete dominance (simple
Mendelian inheritance) over a recessive traitIncomplete dominanceCodominanceIn general terms, a gene contributes to production or expression of some trait or character (a
phene), e.g. the color of one's
iris. A locus is similar, but more loosely defined: since phenes are usually readily apparent but determining which genes contribute to them is a complicated process, loci are simply locations in the
genome which are known to be directly related to expression of defined phenes. Most loci can eventually be assigned to specific genes, but there is no straightforward 1:1 relationship between loci and genes, and whereas a gene always encodes for a
protein, a locus might be in a
noncoding DNA sequence.
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