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

The correct option is A 1 : 4 : 6 : 4 : 1

When the trait is controlled by one or more genes, the dominant alleles of which show a cumulative effect, i.e., only part of the trait is expressed by single dominant allele and expression of the full trait requires the presence of all dominant allele, it is quantitative inheritance. The phenotype of offspring depends on a number of dominant alleles. The dihybrid cross ratio for quantitative inheritance is 1 : 4 : 6 : 4 : 1. Option A is correct. The non-allelic gene interaction in which the trait is governed by duplicate genes for which presence of the single dominant gene is enough to produce the dominant trait, the dihybrid ratio becomes 15 : 1. Here, all genotypes carrying a single/multiple dominant genes show dominant phenotype. Dominant epistasis is the non-allelic gene interaction where the presence of one dominant gene masks the expression of another dominant gene, dihybrid ratio becomes 12 : 3 : 1. Complementary genes are the non-allelic genes which have their independent effect but produce a new trait when their dominant forms are present together. A dihybrid cross of complementary genes gives 9 : 7 phenotypic ratio.