A parent with an `S_1S_2` genotype exhibiting sporophytic self - incompatibility . Which of the following plant genotypes of the pollen grains of the same species it can fertilize ?

Options

A. `S_1S_3`
B. `S_2S_3`
C. `S_3S_4`
D. `S_1S_4`

Answer

To solve the question regarding a parent with an `S1S2` genotype exhibiting sporophytic self-incompatibility, we need to analyze which pollen grain genotypes can successfully fertilize the ovules of this parent plant.

### Step-by-Step Solution:

1. **Understanding Sporophytic Self-Incompatibility**:
- In sporophytic self-incompatibility, the stigma of the flower recognizes the genotype of the pollen grain. If the pollen grain has a genotype that matches either of the alleles present in the stigma (in this case, `S1` or `S2`), it will not germinate.

2. **Identifying the Parent Genotype**:
- The parent plant has the genotype `S1S2`. This means that the stigma will reject any pollen that has either `S1` or `S2` alleles.

3. **Evaluating Pollen Genotypes**:
- For successful fertilization, the pollen grain must have a genotype that does not include `S1` or `S2`. Therefore, we need to look for pollen genotypes that are different from both `S1` and `S2`.

4. **Analyzing the Options**:
- Let's evaluate the provided options:
- **Option 1**: `S1S3` - Contains `S1`, so it cannot fertilize.
- **Option 2**: `S2S3` - Contains `S2`, so it cannot fertilize.
- **Option 3**: `S3S4` - Contains neither `S1` nor `S2`, so it can fertilize.
- **Option 4**: `S1S4` - Contains `S1`, so it cannot fertilize.

5. **Conclusion**:
- The only genotype that can successfully fertilize the `S1S2` parent is `S3S4` (Option 3). Therefore, the correct answer is **Option 3**.