Question

Describe the dihybrid cross with the help of checker board.

Hint:

In a dihybrid cross, the phenotypic ratio for two heterozygous parents is 9:3:3:1.

Answer 1

A dihybrid cross is a genetic cross between two individuals that involves the inheritance of two traits. The two traits are controlled by two different genes, each with two alleles (dominant and recessive). This cross follows the principles of Mendelian inheritance. In order to predict the genetic outcome of a dihybrid cross, we use a Punnett square or checkerboard. Here's a step-by-step explanation: 
 

Step 1: Assigning Alleles and Parental Genotypes
Consider two traits: 
- Trait 1: Seed color (Yellow - Y, Green - y) 
- Trait 2: Seed shape (Round - R, Wrinkled - r)
Assume both parents are heterozygous for both traits (YyRr). 
 

Step 2: Gamete Formation
Each parent can produce four different types of gametes, formed by the independent assortment of alleles: 
- Parent 1 (YyRr) can produce the following gametes: YR, Yr, yR, yr 
- Parent 2 (YyRr) can produce the same gametes: YR, Yr, yR, yr
 

Step 3: Setting up the Punnett Square (Checkerboard)
Now, set up a 4x4 Punnett square, where each gamete from one parent is placed along the top and the other parent's gametes along the side. The results are as follows: 
\[ \begin{array}{c|c c c c} & YR & Yr & yR & yr \\ \hline YR & YYRR & YYRr & YyRR & YyRr \\ \hline Yr & YYRr & YYrr & YyRr & Yyrr \\ \hline yR & YyRR & YyRr & yyRR & yyRr \\ \hline yr & YyRr & Yyrr & yyRr & yyrr \\ \hline \end{array} \]

Step 4: Genotypic and Phenotypic Ratios
- Genotypic ratio: 1 YYRR : 2 YyRR : 2 YYRr : 4 YyRr : 1 YYrr : 2 Yyrr : 1 yyRR : 2 yyRr : 1 yyrr.
- Phenotypic ratio: 9 Yellow and Round : 3 Yellow and Wrinkled : 3 Green and Round : 1 Green and Wrinkled.