A complementary gene is one of two or more genes that, when present together, create qualitatively diverse effects from each of their individual effects.
The complementary gene is the result of the interaction of two dominant non-interallelic genes, each of which has its own effect, but when they interact, a new trait emerges, and the Mendelian ratio of 9:3:3:1 is transformed to 9:7 because of complementation of the both genes.
Complementary Genes
Complementary genes are a kind of gene interaction in which two genes interact to produce a specific phenotype or observable trait. The term complementary refers to the relationship that exists between the two genes which make up a phenotype. The word complementary comes from the Latin word complement, which means “to complete.” Complementary genes are therefore regarded as genes which work together to complete an apparent result.
A non – Mendelian gene interaction is an example of complementary genes. Because such gene interactions sometimes need more than one gene for a specific trait, inheritance patterns for these kinds of gene interactions are complicated. Complementary genes, for example, aid in the control of bloom colour in the sweet pea plants. This indicates that the colour is determined by two various genes interacting in order to “complete a pathway” and reveal a specific flower hue.
Genotypes in the Complementary Genes
Two dominant alleles of the two separate genes complement one another to produce a certain phenotype in complementary genes. One allele in a genotype is typically enough to define the phenotype. Whether the alleles are recessive or dominant determines which allele helps determine the phenotype. The dominant allele influences the trait’s visible outcome. The dominant allele often masks the trait related with recessive alleles, making it impossible to determine the phenotype.
Complementary Gene Action
The dominant alleles of the two genes function together to contribute to phenotype in complementary gene activity. The trait cannot be exhibited if either gene lacks the dominant allele. Both genes require dominant alleles to “complete” the process and create the relevant phenotype.
Sweet Pea Flower Experiment
Bateson and Punnett conducted their studies on Lathyrus odoratus, a purple-flowered sweet pea. They employed two white-flowering cultivars of the plant in their trials. In the first stage of their research, scientists crossed two variants of white sweet pea blossoms, resulting in the first generation of purple flowers.
Bateson and Punnett created the second generation by crossing two of the first generation’s purple blossoms. They found 382 purple – flowered plants with 269 white – flowered plants in the 2nd generation of flowers.
Phenotypic Ratio
Purple flowers had a phenotypic ratio of 9:7 to white flowers. The phenotypic ratio, in general, aids in estimating the or probability possibility of a trait developing in the offspring. Bateson and Punnett were taken aback by the result of 9 purple blooms against 7 white flowers. They were both expecting the phenotypic ratio shown in a dihybrid cross (9 3 3 1), which is really the ratio we find when crossing two genes that affect two separate phenotypes. The phenotype of the sweet pea blossoms revealed that, unlike a dihybrid cross, the two scientists had discovered a novel sort of heredity.
Complementary factors (9:7)
Certain traits have been discovered to be produced by the interplay of two genes passed down from one generation to the next. When two or more genes are found on distinct gene loci and interact to produce a specific or phenotypic trait, they are considered to be complementary genes. However, neither of the genes has its unique phenotypic manifestation. In the absence of the other, they cannot be expressed phenotypically. When one or both genes are missing, a recessive or alternate character is produced. The genes, in this case, are considered as complementary genes.
Conclusion
Complementary genes are non-allelic genes that can interact with one another to produce a composite characteristic. Despite being dominant, each gene within a complementary pair cannot generate independent phenotypes. Two sweet pea kinds, for example, may produce white blossoms in successive generations. The F1 generation, however, will yield purple flowers if the two white flower colour variations are crossed. The F2 generation, on the other hand, develops both and white purple flowers in a phenotypic ratio of 9 purple:7 white. The purple colour is created by the interaction of two genes that are in a dominant state.