Dominance and Recessivity


Dominance and recessivity are not intrinsic properties of genes or alleles but describe, in diploid organisms, the pattern of occurrence of a phenotypic trait with respect to the possible combinations of two alleles. If the trait is present in the heterozygote, it is said to be dominant or semidominant, and if it is present only in one of the homozygotes, it is recessive.

Keywords: dominance; semidominance; recessivity; haploinsufficiency; gain of function

Figure 1.

Mendel's experiment demonstrating the properties of dominance and recessivity. Cross‐pollination between pure‐bred lines of peas grown from round and wrinkled seeds gave rise only to round seeds (F1 generation). However, these F1 plants produced wrinkled seeds as well as round seeds when intercrossed, in a ratio of about three round to one wrinkled (F2 generation). Mendel explained this pattern by postulating that the phenotype was determined by the combination of factors R and r. The round is dominant over the wrinkled trait because the round trait is manifested in the heterozygote Rr. Conversely, wrinkled is recessive to round.

Figure 2.

Dominance relationships between a pair of alleles A and B. (a, b) Phenotypes corresponding to the different genotypes AA, AB and BB are indicated by filled rectangles of different tones. (c) In many dominantly inherited diseases, the phenotype associated with the homozygous mutant BB has not been observed; hence it is not known whether allele B is a true dominant or semidominant, with respect to A.

Figure 3.

Typical pedigrees showing autosomal dominant and autosomal recessive inheritance. Affected and unaffected individuals are denoted by filled and open symbols (square, male; circle, female) respectively. (a) Autosomal dominant inheritance of mutant allele B. Transmission of the phenotype occurs vertically between generations. On average, 50% of the offspring of an affected individual are themselves affected, irrespective of sex. (b) Autosomal recessive inheritance of mutant allele B. Consanguinity is frequent, as shown here (closely spaced parallel lines). Usually only a single sibship is affected, with previous and succeeding generations free of the disease. (c) If there is extensive inbreeding or the recessive mutant allele B is very common, pseudodominant inheritance may occur.

Figure 4.

Relationship between protein level and metabolic activity. Most proteins act at the asymptotic end of the activity curve. A 50% reduction in protein compared with the wild‐type level, caused by a heterozygous loss‐of‐function mutation, results in a reduction in activity of less than 10% (assumed to reflect the phenotype); complete loss of the protein abolishes activity. Hence the phenotype of the heterozygote resembles wild type and the mutation is recessive.

Figure 5.

Common mechanism of dominant negative mutation. (a) Dimerization mediated by the left half of the normal monomeric protein activates the function of the right half (shown as a change to shaded fill). (b) Heterozygous mutation that abolishes the activation domain but does not affect dimerization will cause half of the normal protein to become sequestered into nonproductive signaling complexes.


Further Reading

Fincham JRS (1990) Mendel – now down to the molecular level. Nature 343: 208–209.

Herskowitz I (1987) Functional inactivation of genes by dominant negative mutations. Nature 329: 219–222.

Hurst LD and Randerson JP (2000) Dosage, deletions and dominance: simple models of the evolution of gene expression. Journal of Theoretical Biology 205: 641–647.

Keightley PD (1996) A metabolic basis for dominance and recessivity. Genetics 143: 621–625.

Muller HJ (1932) Further studies on the nature and causes of gene mutations. In: Jones DF (ed.) Proceedings of the Sixth International Congress of Genetics, pp. 213–255. Menasha, WI: Brooklyn Botanic Gardens.

Orel V (1996) Gregor Mendel. The First Geneticist. Oxford, UK: Oxford University Press.

Orr HA (1991) A test of Fisher's theory of dominance. Proceedings of the National Academy of Sciences of the United States of America 88: 11413–11415.

Siracusa LD (1994) The agouti gene: turned on to yellow. Trends in Genetics 10: 423–428.

Wilkie AOM (1994) The molecular basis of genetic dominance. Journal of Medical Genetics 31: 89–98.

Zlotogora J (1997) Dominance and homozygosity. American Journal of Medical Genetics 68: 412–416.

Web Links

Genew: Human Gene Nomenclature Database Search Engine‐bin/nomenclature/

OMIM (Online Mendelian Inheritance in Man). A catalog of human genes and genetic disorders

Aquaporin 2 (collecting duct) (AQP2); Locus ID: 359. LocusLink:

GNAS complex locus (GNAS); Locus ID: 2778. LocusLink:

Luteinizing hormone/choriogonadotropin receptor (LHCGR); Locus ID: 3973. LocusLink:

Myocilin, trabecular meshwork inducible glucocorticoid response (MYOC); Locus ID: 4653. LocusLink:

Prion protein (p27–30) (Creutzfeldt–Jakob disease, Gerstmann‐Straussler‐Scheinker syndrome, fatal familial insomnia) (PRNP); Locus ID: 5621. LocusLink:

Aquaporin 2 (collecting duct) (AQP2); MIM number: 107777. OMIM:‐post/Omim/dispmim?107777

GNAS complex locus (GNAS); MIM number: 139320. OMIM:‐post/Omim/dispmim?139320

Luteinizing hormone/choriogonadotropin receptor (LHCGR); MIM number: 152790. OMIM:‐post/Omim/dispmim?152790

Myocilin, trabecular meshwork inducible glucocorticoid response (MYOC); MIM number: 601652. OMIM:‐post/Omim/dispmim?601652

Prion protein (p27‐30) (Creutzfeldt–Jakob disease, Gerstmann‐Straussler‐Scheinker syndrome, fatal familial insomnia) (PRNP); MIM number: 176640. OMIM:‐post/Omim/dispmim?176640

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Wilkie, Andrew OM(Jan 2006) Dominance and Recessivity. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0005475]