Question

Phenotypic and genotypic ratio in F${}_2$ generation in incomplete dominance is

• A. 1 : 2 : 1 and 1 : 2 : 1
• B. 9 : 6 and 1 : 2 : 1
• C. 9 : 6 and 3 : 1
• D. 9 : 3 : 3 : 1 and 1 : 2 : 1 : 4 : 1 :1 : 2 : 1 : 2 : 1

Answer 1

The correct option is A 1 : 2 : 1 and 1 : 2 : 1

Incomplete dominance is the condition when none of factors of a gene is dominant, the phenotype of heterozygous dominant individual is blend of dominant and recessive traits. For example flower colour in Mirabilis jalapa shows incomplete dominance and the monohybrid cross between two pure varieties gives 1 : 2 : 1 phenotypic ratio in F${}_2$ generation which is 3 : 1 in otherwise dominant traits. This is because the heterozygous genotypes do not show the dominant trait but they are blend of dominant and recessive phenotype. A cross between two pure breeding genotypes that differ in two pairs of trait (dihybrid cross) followed by selfing of F${}_1$ hybrid gives 9 : 3 : 3 : 1 phenotypic ratio and 1 : 2 : 1 : 4 : 1 : 1 : 2 : 1 : 2 : 1 genotypic ratio. Option B and C show both dihybrid (9 : 6), a dihybrid cross gives total 16 types which make these two options wrong.