Question

Phenotypic and genotypic ratio in $F_2$ generation is similar in the case of

• A. complete dominance
• B. incomplete dominance
• C. polygenic inheritance
• D. epistasis

Answer 1

The correct option is B incomplete dominance

Incomplete dominance is the phenomenon of neither of the two alleles being completely dominant. So, the expression in the hybrid is intermediate between the expressions of the two alleles in a homozygous state. $F_2$ phenotypic ratio is 1: 2: 1, similar to the genotypic ratio.

Complete dominance occurs when one allele of a gene completely masks another.
The phenotypic ratio is 3:1 and the genotypic ratio is 1 : 2: 1.

Polygenic inheritance refers to the type of inheritance when one character is controlled by two or more genes. Hence, two or more genes are responsible for controlling the expression of a particular phenotype. The $F_2$ dihybrid ratio for kernel colour in wheat is found to be 1: 4: 6: 4: 1 which is different from its genotypic ratio 1:2:1:2:4:2:1:2:1.

Epistasis is a condition where the expression of one gene is affected by the expression of one or more independently inherited genes. For example, in dominant epistasis, the $F_2$ dihybrid phenotypic ratio for fruit colour in summer squash is found to be 12:3:1 which is different from its genotypic ratio 1:2:1:2:4:2:1:2:1.