Question

What is the ratio of recombinant to parental phenotypes in the Mendel’s dihybrid cross?

• A. 5 : 3
• B. 9 : 7
• C. 3 : 5
• D. 7 : 9

Answer 1

The correct option is C 3 : 5

The phenotypic ratio in Mendel’s dihybrid cross is 9 : 3 : 3 : 1.
Let us take the example of cross between parents pureline for contrasting traits of two characters: seed color and seed shape.
The F2 phenotypic ratio is:-
yellow round : yellow wrinkled : green round : green wrinkled = 9 : 3 : 3 : 1, as shown below.
$\begin{array}{ccccc}\text{Gametes}& \text{RY}& \text{Ry}& \text{rY}& \text{ry}\\ \text{RY}& \text{RRYY}& \text{RRYy}& \text{RrYY}& \text{RrYy}\\ & \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Round, yellow)}\\ \text{Ry}& \text{RRYy}& \text{RRyy}& \text{RrYy}& \text{Rryy}\\ & \text{(Round, yellow)}& \text{(Round, green)}& \text{(Round, yellow)}& \text{(Round, green)}\\ \text{rY}& \text{RrYY}& \text{RrYy}& \text{rrYY}& \text{rrYy}\\ & \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Wrinkled, yellow)}& \text{(Wrinkled, Yellow)}\\ \text{ry}& \text{RrYy}& \text{RrYy}& \text{rrYY}& \text{rrYy}\\ & \text{(Round, yellow)}& \text{(Round, green)}& \text{(Wrinkled, yellow)}& \text{(Wrinkled, green)}\end{array}$
Recombinant phenotype = 3 (yellow, wrinkled seeds) + 3 (green, round seeds) = 6
Parental phenotype = 9 (yellow, round seeds) + 1 (green, wrinkled seeds) = 10
The ratio of recombinant to parental phenotypes = 6 : 10 = 3 : 5