Question

9:6:1 $F_2$ generation is obtained in case of
A. Polymeric genes
B. Pleiotropic genes
C. Supplementary genes
D. Recessive epistasis

Answer 1

Hint: A gene is a fundamental unit of heredity in a living organism. Genes generally come from the parents. Genes composed of the data required to build and maintain cells and pass genetic information to offspring

Complete answer:
Genetic interaction networks stand for the functional interactions between pairs of genes in an organism which are useful for understanding the relationship between genotype and phenotype. The best part of genes do not code for particular phenotypes. In its place, phenotypes frequently result from the interaction between several genes. In the case of humans, Each individual carries about 4million genetic variants and polymorphisms, Interactions between genetic variants, all along with the environmental conditions, are possible to play a major role in deciding the phenotype that originates from a given genotype. Genetic interaction networks help out to understand genetic interactions by identifying the interactions between pairs of genes.

A. Polymeric genes – they are generally two independent dominant genes present as homozygous or heterozygous conditions, that have related phenotypic effect when present individually but produce a cumulative or double effect when found together. In the $F_2$ generation 9:6:1 ratio is obtained from this.
B. Pleiotropic genes – The capacity of a gene to have multiple phenotypic effects or as it influences a number of characters simultaneously is generally known as pleiotropy and the genes are termed as Pleiotropic genes.
C. Supplementary genes - Two independent pairs of genes that can interact to produce a new trait jointly but each dominant gene alone gives its own trait, and are usually called as Supplementary genes. In $F_2$ generation they give the ratio as 9:3:4.
D. Recessive epistasis – Recessive allele in homozygous condition masks the consequence of dominant allele and are called recessive epistasis. In the $F_2$ generation the ratio obtained is 9:3:4 ratio.

Hence, the correct answer is option (A)

Note: Mendel and other workers understood that characters are governed by single genes but later on it was discovered that many characters are governed by two or more genes. That type of genes affect the development of concerned characters in various ways.