Question

Which of the following depicts Mendel's dihybrid ratio?
(A) 3:1
(B) 9:3:3:1
(C) 9:7
(D) 15:1

Answer 1

Hint: Mendel took a pair of contradicting traits together for dihybrid crossing which showed two distinguished phenotypic and genotypic ratios. The phenotypic ratio here is known as Mendel's dihybrid ratio.

Complete answer:
Mendel's dihybrid cross represents the cross between two different lines that differs in two observed traits. The ratio indicating this cross is 9:3:3:1. According to Mendel's statement, there is a relationship of completely dominant- recessive traits between these alleles.

Additional Information: Let us try to understand the concept of dihybrid cross using a Punnett square of dimensions 16:

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

In the case of separate chromosomes, each allele pair shows independent segregation. In ${ F }_{ 1 }$ generation four identical offspring are produced whereas in F2, produced by crossing individuals of ${ F }_{ 1 }$, shows a phenotypic ratio of 9:3:3:1.
Here,
9 represent individuals of both dominant traits
3 represents individuals displaying the first dominant trait and the second recessive trait
3 represents individuals of the first recessive traits and second dominant traits
1 represents individuals with both recessive traits.
So, the correct answer is ‘(B) 9:3:3:1’.

Note: The "di" in dihybrid cross indicates the involvement of two traits, in this case, R and Y, and the "hybrid" means that each of the two traits has two distinguished alleles (here R and r, or Y and y). Cross means that the mother and father are Combining or crossing their genetic information. In the case of a dihybrid cross, the genotypic ratio is 1:2:1:2:4:2:1:2:1.