Dominance (genetics)

Dominance (genetics)

Dominance in genetics is a relationship between alleles of one gene, in which the effect on phenotype of one allele masks the contribution of a second allele at the same locus. The first allele is dominant and the second allele is recessive. For genes on an autosome (any chromosome other than a sex chromosome), the alleles and their associated traits are autosomal dominant or autosomal recessive.

History

The concept of dominance was introduced by Gregor Mendel. Though Mendel, "The Father of Genetics", first used the term in the 1860s, it was not widely known until the early 20th century. Mendel observed that, for a variety of traits of garden peas having to do with the appearance of seeds, seed pods, and plants, there were two discrete phenotypes, such as round versus wrinkled seeds, yellow versus green seeds, red versus white flowers or tall versus short plants.

Types of Dominance

Dominance is a key concept in Mendelian inheritance and classical genetics. The dominant allele codes for a functional protein whereas the recessive allele does not. A classic example of dominance is the inheritance of seed shape in peas. 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 individuals have round peas and the rr individuals have wrinkled peas.

Complete Dominance

In complete dominance, the effect of one allele in a heterozygous genotype completely masks the effect of the other. The allele that masks the other is said to be dominant to the latter, and the allele that is masked is said to be recessive to the former.

Co-dominance

In co-dominance, the "dominant" alleles are expressed simultaneously in the phenotype.

Incomplete Dominance

In incomplete dominance, the phenotype is a blend of the two alleles.

See Also

• Genotype
• Phenotype
• Heterozygote advantage
• Polymorphism (biology)

References

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