Question

In the dihybrid cross, the two parental genotypes are AABB and aabb. The genotype of all F1 plants is AaBb. What phenotypes ration will be observed in the F2 Generation?
A) 8:4:2:1
B) 1:1:1:1
C) 4:2:2:1
D) 1:2:2:1
E) 9:3:3:1

Answer 1

Hint:Dihybrid cross is a cross between the two different characters/genes that differ in two observed traits. For example – the cross between the dominant yellow coloured seeds and Round seeds (RRYY) and green coloured seeds and wrinkled seeds (rryy). Here there are two traits involved in this cross i.e. seed colour and seed shape that’s why it is called a dihybrid cross.

Complete answer:
>In the dihybrid cross given in the question the two parental genotypes are – AABB and aabb.
>The genotype of all F1 plants is AaBb.
>The cross between the members of F1 generation is called as F2 generation that means the cross between AABB and AbBb.
a)

Parents	AABB	×	aabb
Gametes	AB		ab

F1 generation - AaBb

b)

Parents	AaBb	×	AaBb
Gametes	AB Ab aB ab		AB Ab aB ab

F2 generation-

	AB	Ab	aB	ab
AB	AABB	AABb	AaBB	AaBb
Ab	AABb	AAbb	AaBb	Aabb
aB	AaBB	AaBb	aaBB	aaBb
ab	AaBb	Aabb	aaBb	aabb

The 9 offsprings represented by pink colour have same phenotypes, 3 offsprings represented by blue colour have same phenotypes, 3 phenotypes represented by green colour have same phenotypes and one offspring represented by green colour have a different phenotype.

In total 16 offsprings are obtained and the phenotypic ratio of F2 generation is 9:3:3:1.

Therefore, it has been clear from the above discussion that in the dihybrid cross, the two parental genotypes are AABB and aabb. The genotype of all F1 plants is AaBb. 9:3:3:1 phenotypic ratio will be observed in the F2 generation.

Hence, option E is the correct answer for this question.

Note:The genetic makeup of any individual is called a genotype. Genotype is a set of heritable genes that can be passed down from parents to the offsprings. And the observable physical property of an organism is called its phenotype such as organism’s behaviour, appearance, development, etc.