Dominant gene

In genetics, the term dominant gene refers to the allele that causes a phenotype that is seen in a heterozygous genotype. Every person has two copies of every gene, one from mother and one from father. If a genetic trait is dominant, a person only needs to inherit one copy of the gene for the trait to be expressed.

Dominance/recessiveness refers to phenotype, not genotype. Consider sickle cell anemia as an example. The sickle cell genotype is caused by a single base pair change in the beta-globin gene: normal=GAG (glu), sickle=GTG (val). There are several phenotypes associated with the sickle genotype: 1) anemia (a recessive trait), 2) blood cell sickling (partially dominant), 3) altered beta-globin electrophoretic mobility (codominant), and 4) resistance to malaria (dominant). This example demonstrates that one can only refer to dominance/recessiveness with respect to individual phenotypes.

A dominant gene when written in a genotype is always written before the recessive gene in a heterozygous pair. A heterozygous genotype is written Aa, not aA.

Codominance/ Incomplete Dominance
In certain cases, a "blend" of genes will occur because neither of the two genes of a genotype are dominant over the other. As an example, in blood cells, the trait for blood type has three different alleles: type A, type B, or type i, with i being recessive. If a father passes a gamete with the allele of type A and the mother passes on type B, then codominance results, with the offspring being type AB since neither allele type dominates the other.

Incomplete dominance occurs when certain of the recessive gene appears within the phenotype of the organism, causing a blend in between both the dominant and recessive gene.

Dominant negative
Most loss-of-function mutations are recessive. However, some are dominant and are called "dominant negative" mutations. Typically, a dominant negative mutation results in a protein that is structurally similar to the wild-type protein, but which has lost the normal function. Such proteins may be competitive inhibitors of the normal protein function.

See also:

 * Recessive gene
 * Incomplete dominance
 * Codominance
 * Dominance relationship
 * Autosomal dominant

Gen dominante 優性遺伝 우성 유전자 Dominant (genetica) Gene dominante