What percentage of pea seeds would have intermediate size of starch grains in `F_(2)` generation?

Options

A. 0
B. 0.25
C. 0.5
D. 0.75

Answer

To determine the percentage of pea seeds that would have intermediate size of starch grains in the F2 generation, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Trait and Alleles**:
- The trait in question is the size of starch grains in pea seeds, which is controlled by a single gene (B gene).
- There are two alleles: the dominant allele (B) for large starch grains and the recessive allele (b) for small starch grains.

2. **Set Up the Parental Generation (P Generation)**:
- The parental generation consists of two pure breeds: one homozygous dominant (BB) and one homozygous recessive (bb).
- Thus, the cross is BB (large) x bb (small).

3. **Determine the F1 Generation**:
- When these two parental plants are crossed, all offspring in the F1 generation will be heterozygous (Bb).
- The phenotype of the F1 generation will show the dominant trait, which is large starch grains.

4. **Understand Incomplete Dominance**:
- In this scenario, we are dealing with incomplete dominance, meaning that the heterozygous phenotype (Bb) will show an intermediate trait rather than just the dominant trait.
- Therefore, the Bb genotype will result in an intermediate size of starch grains.

5. **Self-Pollination of F1 Generation**:
- The F1 generation (Bb) will self-pollinate to produce the F2 generation.
- The cross will be Bb x Bb.

6. **Create a Punnett Square for F2 Generation**:
- Set up a Punnett square for the cross Bb x Bb:
```
B b
-----------
B | BB | Bb |
-----------
b | Bb | bb |
-----------
```
- The genotypes produced will be:
- 1 BB (homozygous dominant)
- 2 Bb (heterozygous)
- 1 bb (homozygous recessive)

7. **Determine the Phenotypic Ratio**:
- The phenotypic ratio from the Punnett square is 1 (large) : 2 (intermediate) : 1 (small).
- This means that out of the four possible phenotypes, 2 will exhibit the intermediate size.

8. **Calculate the Percentage**:
- To find the percentage of seeds with intermediate size, we take the number of intermediate phenotype (2) divided by the total number of phenotypes (4):
\[ \text{Percentage of intermediate size} = \left(\frac{2}{4}\right) \times 100 = 50\% \]

### Final Answer:
**50% of the pea seeds would have intermediate size of starch grains in the F2 generation.**

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