Question

In which of the following, the phenotypic and genotypic ratios are similar in the $F_2$ generation?

A. Incomplete dominance
B. Dominance
C. Co-dominance

• A. A, B and C
• B. B and C
• C. Only A
• D. Both A and C

Answer 1

The correct option is D Both A and C

In incomplete dominance and co-dominance, a similar phenotypic and genotypic ratio of 1: 2: 1 is seen in the $F_2$ generation.

In incomplete dominance and co-dominance, unlike dominance, the $F_1$ generation hybrid does not resemble either of the two parents. Hence, there is deviation of phenotypic ratio
from 3: 1 to 1: 2: 1.

In incomplete dominance, the dominant allele fails to suppress the recessive allele and hence an intermediate phenotype is seen in the hybrid.

This is observed in snapdragon. When a plant with red flowers is crossed to a plant with white flowers, the progeny produces flowers of pink colour.

In co-dominance, both alleles of the gene are dominant and express independently in the heterozygous condition and the $F_1$ hybrid resembles both the parents. It is observed in cattle. When cattle of red coat are crossed with cattle of white coat, the progeny has red and white coat together and it is called roan cattle.

Hence, incomplete dominance and co-dominance deviate from the Law of Dominance given by Mendel.

According to the Law of Dominance, the $F_1$ hybrid resembles either of the two parents.
The phenotypic and genotypic ratio in case of dominance will be 3: 1 and 1: 2: 1 respectively.