Dominance (genetics)

In <a href="/facts/Genetics/bu8wne0A">genetics</a>, dominance is the phenomenon of one variant (<a href="/facts/Allele/8FxCS9KA">allele</a>) of a <a href="/facts/Gene/e1swwPY6">gene</a> on a <a href="/facts/Chromosome/FRGf11FC">chromosome</a> masking or overriding the <a href="/facts/Phenotype/vxWXKGLj">effect</a> of a different variant of the same gene on <a href="/facts/Homologous_chromosome/hktsBhyx">the other copy of the chromosome</a>. The first variant is termed dominant and the second is called recessive. This state of having <a href="/facts/Heterozygosity/XzEJ5gPp">two different variants</a> of the same gene on each chromosome is originally caused by a <a href="/facts/Mutation/Ee4NnWbY">mutation</a> in one of the genes, either new (de novo) or <a href="/facts/Heredity/t0aMmRWx">inherited</a>. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (<a href="/facts/Autosomes/uN3B2AhI">autosomes</a>) and their associated traits, while those on <a href="/facts/Sex_chromosomes/PGYGkTQM">sex chromosomes</a> (allosomes) are termed <a href="/facts/X-linked_dominant/RmeTdfeP">X-linked dominant</a>, <a href="/facts/X-linked_recessive/HDoKvzId">X-linked recessive</a> or <a href="/facts/Y-linked/lvAXoQYz">Y-linked</a>; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child (see <a href="/facts/Sex_linkage/buXJkWJg">Sex linkage</a>). Since there is only one <a href="/facts/Y_chromosome/nBDd0Vlg">Y chromosome</a>, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance, such as incomplete dominance, in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance, in which different variants on each chromosome both show their associated traits.
Dominance is a key concept in <a href="/facts/Mendelian_inheritance/v2038wkl">Mendelian inheritance</a> and <a href="/facts/Classical_genetics/SwtEeqBW">classical genetics</a>. Letters and <a href="/facts/Punnett_squares/2CFbg0XX">Punnett squares</a> are used to demonstrate the principles of dominance in teaching, and the upper-case letters are used to denote dominant alleles and lower-case letters are used for recessive alleles. An often quoted example of dominance is the inheritance of <a href="/facts/Seed/a4xGSLxJ">seed</a> shape in <a href="/facts/Pea/hlndxpId">peas</a>. Peas may be round, associated with allele R, or wrinkled, associated with allele r. In this case, three combinations of alleles (genotypes) are possible: RR, Rr, and rr. The RR (<a href="/facts/Homozygous/XzEJ5gPp">homozygous</a>) individuals have round peas, and the rr (homozygous) individuals have wrinkled peas. In Rr (<a href="/facts/Heterozygous/XzEJ5gPp">heterozygous</a>) individuals, the R allele masks the presence of the r allele, so these individuals also have round peas. Thus, allele R is dominant over allele r, and allele r is recessive to allele R.
Dominance is not inherent to an allele or its traits (<a href="/facts/Phenotype/vxWXKGLj">phenotype</a>). It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth. Additionally, one allele may be dominant for one trait but not others. Dominance differs from <a href="/facts/Epistasis/bJAJL90w">epistasis</a>, the phenomenon of an allele of one gene masking the effect of alleles of a different gene.

Dominance (genetics) open-in-new

Dominance (genetics)