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

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.