Number of kinds of genotypes in `F_(2)` generation of mendel's dihybrid cross

Options

A. 4
B. 9
C. 2
D. 1

Answer

To determine the number of kinds of genotypes in the F2 generation of Mendel's dihybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Dihybrid Cross**: A dihybrid cross involves two traits, each controlled by different genes. For example, consider two traits: seed color (yellow or green) and seed shape (round or wrinkled).

2. **Identify Parental Genotypes**: In Mendel's classic experiments, he used true-breeding plants. For our example, we can denote the parental genotypes as:
- Yellow round (YYRR)
- Green wrinkled (yyrr)

3. **F1 Generation**: When these two true-breeding plants are crossed, all offspring (F1 generation) will be heterozygous for both traits (YyRr), exhibiting the dominant phenotypes (yellow and round).

4. **F2 Generation**: The F1 generation is then self-fertilized (YyRr x YyRr) to produce the F2 generation.

5. **Punnett Square Analysis**: Construct a 4x4 Punnett square to visualize the combinations of alleles from the F1 generation. This leads to the following combinations:
- YYRR
- YYRr
- YyRR
- YyRr
- yyRR
- yyRr
- Yyrr
- yyrr

6. **Count Genotypes**: From the combinations above, we can list the unique genotypes:
- YYRR
- YYRr
- YyRR
- YyRr
- yyRR
- yyRr
- Yyrr
- yyrr
- YyRr (already counted)

After counting, we find there are 9 unique genotypes.

7. **Conclusion**: Therefore, the number of kinds of genotypes in the F2 generation of Mendel's dihybrid cross is 9.

### Final Answer:
The number of kinds of genotypes in the F2 generation of Mendel's dihybrid cross is **9**.

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