Question

In quantitative inheritance,$F_2$ratio obtained in a dihybrid cross is
a. ${1:4:6:4:1}$
b. ${15:1}$
c. ${12:3:1}$
d. ${9:7}$

Answer 1

Quantitative inheritance is a term used in genetics which means the combined result when more than one (multiple) factors are combined to give distinctive traits. A dihybrid cross can be defined as a cross between two different genes.

Complete answer:

Option (A) is correct.
When a trait is controlled by more than one gene called polygenes in which dominant alleles show a cumulative effect where part of the trait is controlled by a single dominant allele and the whole trait’s expression requires the cumulative effect of all the dominant alleles. This is called quantitative inheritance. So, the phenotype of offspring depends on the dominant alleles. Therefore, the dihybrid cross-ratio in$F_2$.generation is ${1:4:6:4:1}$ in the case of quantitative inheritance.

Option (B) is incorrect.
The dihybrid ratio ${15:1}$ exists in the case of duplicate dominant epistasis where the interaction of the non-allelic genes takes place and the expression of a trait is governed by the duplicate genes for which a single dominant gene is sufficient to produce the dominant trait.

Option (C) is incorrect.
The dihybrid ratio ${12:3:1}$ exists in the case of dominant epistasis in which if one gene is dominant then it masks the phenotype of the other gene.

Option (D) is incorrect.
The dihybrid ratio${9:7}$exists in the case of duplicate recessive epistasis wherein when either of the genes is homozygous recessive then it masks the phenotype of the other gene.

Hence, the correct answer is option (A).

Note: In the $F_2$ generation of quantitative inheritance, the dihybrid ratio comes out to be${1:4:6:4:1}$ which indicates that the overall expression of a trait is controlled by polygenes.