Question

In a monohybrid cross between two heterozygous parents (\(Aa \times Aa\)), what is the genotypic ratio among the offspring?

• A. 1:1.
• B. 1:2:1.
• C. 3:1.
• D. 9:3:3:1.

Hint:

In a monohybrid cross between heterozygous parents, the genotypic ratio is always \(1:2:1\), while the phenotypic ratio is \(3:1\).

Answer 1

The Correct Option is B

Step 1: Setting up the Punnett square.
The genotypes of the parents are \(Aa\) and \(Aa\). The Punnett square is set up as follows: \[ \begin{array}{c|c|c} & A & a
\hline A & AA & Aa
a & Aa & aa
\end{array} \] Step 2: Calculating the genotypic ratio.
From the Punnett square, the offspring have the following genotypes: \(AA\): 1 individual. \(Aa\): 2 individuals. \(aa\): 1 individual. The genotypic ratio is therefore: \[ 1 : 2 : 1. \] Step 3: Explanation of options.
Option (A): Incorrect. This represents an equal distribution between two genotypes, which is not the case. Option (B): Correct. The genotypic ratio for a monohybrid cross is \(1:2:1\). Option (C): Incorrect. This represents the phenotypic ratio, not the genotypic ratio. Option (D): Incorrect. This represents the phenotypic ratio for a dihybrid cross, not a monohybrid cross. \[ \therefore \text{The correct genotypic ratio is: } 1 : 2 : 1. \]