Question

In a monohybrid cross, which of the following is always completely heterozygous?

• A. $\text{F}_1$ generation
• B. $\text{F}_2$ generation
• C. $\text{F}_3$ generation
• D. P generation

Hint:

Selfing the heterozygous $\text{F}_1$ ($Aa$) generation produces the $\text{F}_2$ generation, which segregates in a 1:2:1 genotypic ratio ($AA$ : $Aa$ : $aa$), reducing heterozygosity by 50%.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A monohybrid cross analyzes the inheritance of a single trait.
It begins by crossing two homozygous parent lines (P generation) that carry different alleles for that trait.

Step 2: Detailed Explanation:
- Let the dominant homozygous parent have the genotype $AA$ and the recessive homozygous parent have the genotype $aa$.
- During gametogenesis:
- Parent $AA$ produces only $A$ gametes.
- Parent $aa$ produces only $a$ gametes.
- Fertilization of these gametes yields the first filial ($\text{F}_1$) generation:
\[ AA \times aa \longrightarrow Aa \] - Every individual in this $\text{F}_1$ generation receives one $A$ allele and one $a$ allele, making the generation 100% heterozygous ($Aa$).
- Subsequent generations ($\text{F}_2$, $\text{F}_3$) segregate to produce both homozygous and heterozygous individuals.

Step 3: Final Answer:
The generation that is completely heterozygous in a monohybrid cross is the $\text{F}_1$ generation.