Question

In a complementary gene, interaction calculate the number of phenotype and genotype produced in a cross AaBb X aaBB
A. 1 phenotype, 2 genotypes
B. 2 phenotypes, 4 genotypes
C. 4 phenotypes, 4 genotypes
D. 2 phenotypes, 2 genotypes

Answer 1

In a non-allelic gene interaction, the dominant allele at different loci may complement the other by masking the effect of a recessive allele at respective loci. This results in a complementary or special phenotype and the genes are known as complementary genes. It is an interallelic gene interaction. It is also known as epistasis.

Complete answer: In a complementary gene interaction, both the dominant alleles together form a new phenotype. The genes complement the effect of each other and for the production of a wild phenotype both the genes are important. In this type of interaction, when genotypes such as aaBB, aaBb, Aabb, and aabb produce the same type of phenotype. Therefore, when AaBb and aaBB are crossed, then the gametes produced will be AB, Ab, aB, ab, and aB, aB. Then, the offspring will have four different genotypes- AaBB, aaBb, AaBb, and aaBB. Two types of phenotypes are observed.
Hence, the correct option is (B) 2 phenotypes, 4 genotypes.

Note: The two genes present on the different loci will produce the same effect when present alone and when they are present together, they will interact and form a new trait, and are known as complementary genes. These genes are very important for organisms and are commonly found in many organisms. They produce identical phenotypes and instead of $9:3:3:1$ ratio, they form a $9:7$ ratio. The dominant genes cannot produce an independent trait or character.