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Supplementary Gene

A Supplementary gene is a pair of two or more genes that, when present together, have effects that are fundamentally different from their individual effects.

The Supplementary gene is the result of the interaction of two dominant non-interallelic genes, each of which has its own function; nevertheless, when they interact, a new trait emerges, and the Mendelian ratio of 9:3:3:1 is changed to 9:7 owing to gene complementation.

Supplementary Gene

Supplementary Genes

Definition- Supplementary genes are genes that contain two non-allelic pairs of genes. They're both influencing the same character. 1st gene is dominant and therefore can express on its own among the non-allelic genes. The 2nd gene is also dominant, but it only expresses when the first gene is present.

Supplementary genes are a sort of gene interaction in which two genes work together to produce a certain phenotype or trait. The term Supplementary refers to the link between the two genes that comprise a phenotype. Supplementary is derived from the Latin term complement, which means "to complete." Supplementary genes are thus defined as genes that collaborate to produce an obvious result.

Supplementary genes include non-Mendelian gene interactions. Because such gene interactions frequently require more than one gene to produce a specific feature, inheritance patterns for these types of gene interactions are intricate. Supplementary genes, for example, help influence blossom colour in sweet pea plants. This suggests that the colour is decided by two different genes interacting to "complete a pathway" and display a specific floral hue.

Genotypes in the Supplementary Genes

In Supplementary genes, two dominant alleles of two distinct genes work together to produce a certain phenotype. Typically, one allele in a genotype is sufficient to define the phenotype. Whether the alleles are recessive or dominant determines which allele contributes to the phenotype. The observable outcome of the trait is influenced by the dominant allele. The dominant allele frequently covers the trait associated with recessive alleles, making phenotyping impossible.

Supplementary Gene Action

The dominant alleles of the two genes collaborate to contribute to the phenotype in Supplementary gene activity. The trait cannot be shown if either gene lacks the dominant allele. To "complete" the process and create the desired phenotype, both genes require dominant alleles.

Sweet Pea Flower Experiment

Bateson and Punnett studied the purple-flowered sweet pea Lathyrus odoratus. In their testing, they used two white-flowering varieties of the plant. In the first step of their research, scientists merged two varieties of white sweet pea blooms, 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 detected 382 purple-flowered plants and 269 white-flowered plants in the second generation of flowers.

Phenotypic Ratio

Purple flowers outnumbered white flowers 9:7 in phenotypic ratio. In general, the phenotypic ratio aids in assessing the likelihood of a trait occurring in offspring. The outcome of 9 purple blossoms against 7 white flowers surprised Bateson and Punnett. They were both expecting the phenotypic ratio seen in a dihybrid cross (9:3: 3:1), which occurs when two genes that affect two different phenotypes are crossed. The sweet pea flower phenotype revealed that, in contrast to a dihybrid cross, the two scientists had discovered a new type of inheritance.

Supplementary Factors (9:7)

Certain features have been discovered to be formed by the interaction of two genes that are passed down from generation to generation. Supplementary genes are discovered when two or more genes on different gene loci interact to produce a specific or phenotypic trait. However, neither genes has a distinct phenotypic presentation. They cannot be phenotypically exhibited in the absence of the other. A recessive or alternative character is formed when one or both genes are lacking. In this situation, the genes are classified as Supplementary genes.


Non-allelic genes that interact with one another to form a composite trait are referred to as supplementary genes. Despite being dominant, each gene in a Supplementary pair is incapable of producing independent phenotypes. For example, two sweet pea varieties may yield white flowers in successive generations. The F1 generation will produce purple flowers if the two white flower colour variations are crossed. The F2 generation, on the other hand, produces both and white, purple flowers in a phenotypic ratio of 9 purple:7 white. The purple colour is caused by the interaction of two dominant genes.

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