Complementation

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In genetics, complementation describes the functional addition of two recessive mutations of different genes in such a way that their visible effect is canceled out in the phenotype . Genetic defects can be compensated phenotypically through complementation, because functionality is established at the level of the encoded proteins, while the mutation at the DNA level (the genetic defect) is retained. In the experiment, complementation provides information about the relationship between two gene loci :

With the help of the so-called complementation test , which is also known as the cis-trans test, an attempt can be made to determine whether or not two mutant phenotypes that are similar are caused by a mutation in the same gene.

A recessively inherited phenotype mutant in a trait can be caused in a diploid organism either by the presence of mutated alleles of one and the same gene (same location, gene locus), or by mutations at different loci. If the mutations a and b are at the same gene locus, a diploid, heterozygous organism carrying both mutations (which therefore has an a allele and a b allele, genotype "ab") shows the mutant phenotype. There is also the possibility that the alleles are one and the same mutation (two identical a or b alleles, genotype "aa" or "bb"). A (heterozygous diploid) organism, on the other hand, can appear with the naturally occurring ( wild-type ) phenotype if the mutations a and b are at different gene locations (e.g. genotype AaBb). In this case, the residual activities of the wild-type alleles (A and B) complement each other functionally.