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Complementation (genetics)

The complementary action of different genetic factors. The term usually implies two homologous chromosomes or chromosome sets, each defective because of mutation and unable by itself to promote the normal development or metabolism of the organism, but able to do so jointly when brought together in the same cell. See Chromosome, Mutation

S. Benzer proposed the term cistron for the unit within which mutants do not complement each other. The word gene is often used in the same sense. The usual biochemical function of a cistron, or gene, is to determine the structure of a specific polypeptide component of a protein. Full complementation between different genes is the rule except when, as sometimes in bacteria, the genes form part of a functionally coordinated complex (operon). Allelic mutants (mutants within one gene) show limited complementation in some cases, for example, when certain pairs of mutant polypeptides correct each other's defects through coaggregation in a complex protein. See Genetics, Operon



in genetics, the complementary action of two alleles of a single gene or two different genes of the same chromosomal set.

Interallelic complementation is associated with the synthesis in heterozygotes of two different but functionally similar protein molecules instead of the one protein molecule of homozygotes. Moreover, heterozygotes often have hybrid protein molecules made of polypeptide chains that are synthesized under the control of two different alleles. In heterozygotes with defective mutant alleles, complementation may be expressed in a restoration of the ability to synthesize a normally functioning protein—an ability that would be partly or wholly lost to each mutant separately.

Interallelic complementation seems to be the main cause of monogenic heterosis—the superiority of heterozygotes over homozygotes in viability and rate of growth. Detailed complementation charts have been constructed for the genes of certain viruses, bacteria, and fungi.

Intergenic complementation is a manifestation of the interaction of nonallelic genes (epistasis), whereby a defect expressed in the impairment of a given metabolic process is compensated by other genes. The term “complementarity” is sometimes used in biological literature in a sense similar or identical to complementation.


Fincham, J. Geneticheskaia komplementatsiia. Moscow, 1968. (Translated from English.)



The act of replacing a set by its complement.