In Genetics, What Is Complementation?

Interalleliccomplementation refers to a change in the properties of a heterologous multispecific protein caused by the interaction between subunits encoded by two different mutant alleles. A mixed protein may be more active or weakly complementary than a protein composed of one type of subunit. The AB trait is only exhibited when the genotype is AB-. The presence of aa or bb in the genotype will lead to the ab phenotype. This phenomenon is called gene complementation.

Intergenic complementarity

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Interalleliccomplementation refers to a change in the properties of a heterologous multispecific protein caused by the interaction between subunits encoded by two different mutant alleles. A mixed protein may be more active or weakly complementary than a protein composed of one type of subunit. The AB trait is only exhibited when the genotype is AB-. The presence of aa or bb in the genotype will lead to the ab phenotype. This phenomenon is called gene complementation.

When two non-allele mutant genes are co-located in a heterozygous cell or a local zygote (see bacterial conjugation), the wild-type gene compensates for the defect of the mutant gene and restores the cell's phenotype to its normal role. For example, in Figure a, the cis-trans position effect is shown. In the same cell, a gene A has been mutated, but its gene B is intact, and a gene B on another homologous chromosome has been mutated, but its gene A is It is intact, and because each other compensates for the defect caused by the other's mutant gene, the cell phenotype is normal. If the two mutated genes are on one chromosome, and the two genes on the other homologous chromosome are normal, the results are the same (Figure b). If both mutants are the result of mutations in the gene A locus, then the wild-type gene A is missing when they are located on two homologous chromosomes, so the cell phenotype is mutant (Figure c Cis-transposition effect). If these two mutants are located at the gene A locus of the same chromosome, the cell phenotype is normal because gene A on the other homologous chromosome is intact (Figure d). As shown in the schematic diagram a, the cis-trans position effect is shown, and c, the cis-trans position effect is shown, the combination of genes with two mutations on two homologous chromosomes is called the trans configuration; otherwise, as shown in the schematic b, the cis-trans position effect, and The position effect indicates that a gene combination in which two mutations are located on the same chromosome is called a cis configuration. A test that compares the phenotypes of cis- and trans-configuration cells to determine whether two mutations belong to the same gene is called a c-trans position effect test, referred to as a c-trans test or a complementary test. This complementarity is the complementarity between two genes, so it is also called intergene complementarity. Complementary action also refers to the unilateral compensation of one wild-type gene to another allele-mutated gene in the same cell. Cis-transposition effect test American molecular biologist S. Benzer firstly determined whether a series of tightly-linked fast-lysing mutant rII belonged to one gene in E. coli phage T4 according to the above principle. He first isolated thousands of rII mutants with the same phenotype. Through hybridization, the genetic map of the fine structure of the gene was drawn according to the frequency of recombination. Complementary tests were then performed through mixed phage infection, and the results showed that all r mutants can be divided into two groups: rA and rB (see Gene Mapping). Two mutants that belong to rA or rB have no complementary role in mixed infection. Any rA mutant and any rB mutant have complementary effects in mixed infection, and the phenotype returns to normal. Bunze called a region on the chromosome of each mutant that could not be complementary in the trans configuration called a cistron. The cistron test results indicate that the cistron is the smallest unit of genetic material that must remain intact to have normal physiological functions, so it is actually equivalent to a gene and is a synonym for gene. In addition, Benze refers to the smallest structural unit within a gene that can cause heritable phenotypic changes as a mutant, and the structural unit that cannot be divided by recombination is called a recombinant (see Gene). Intragene complementarityIn organisms such as Neurospora, yeast, E. coli, and Salmonella, it has been found that there is a complementary effect between mutants at different positions within a gene.This complement is called intragene complementarity. This aspect differs from general intergenic complementarity: intergenic complementarity can occur between any two non-alleles, and intragenic complementarity only occurs between several different mutants within the same gene; intergenic complementarity In general, the wild-type phenotype can be completely restored, no matter how far the two genes are. Intragenetic complementation can only restore the phenotype to 25% of the wild type at most, and the closer the mutation sites are, the weaker the complementarity is. A series of mutation sites showing complementarity within genes constitute a complementary group. The peptides encoded by the complementary groups exhibiting intra-gene complementation are all one subunit of an enzyme protein, and this protein is composed of several identical subunits. Therefore, some people imagine that two subunits with structural changes in different parts may aggregate into an enzyme protein with a small amount of normal enzyme activity, which is generally considered to be the molecular basis of complementation in genes. In the complementary test, two chromosomes or chromosome fragments to be tested must be located in the same cell. In bacteria, this can be achieved through bacterial conjugation, transduction, F-factor transfer, phage mixed infection, and other pathways. In eukaryotes, it can be obtained by methods such as cell fusion (see somatic genetics). In genetics research, complementary tests and gene mapping are both the most basic research methods. For example, in Escherichia coli, a series of mutants affecting F-factor transfer function have been obtained. The results of complementary tests on these mutants indicate that there are 13 genes related to conjugation and transfer on F-factor. There are different types of pigmented dry skin disease in humans. The cell fusion method is used to perform complementary tests on the somatic cells of patients with different types of pigmented dry skin disease. At least 7 genes and the occurrence of this skin cancer have been found by 1978 Relevant (see DNA Damage Repair).