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 problem, we need to understand the concept of sporophytic self-incompatibility and how it affects fertilization in plants. Let's break down the solution step by step:

### Step 1: Understand Self-Incompatibility
Self-incompatibility is a mechanism in flowering plants that prevents self-fertilization. In this case, the parent plant has the genotype `S1S2`, which means it carries two different alleles (S1 and S2) for self-incompatibility.

**Hint:** Remember that self-incompatibility is a strategy used by plants to promote genetic diversity by preventing self-pollination.

### Step 2: Identify the Mechanism
In sporophytic self-incompatibility, the pollen grains that can fertilize the ovules must not carry the same S alleles as the stigma. If the pollen grain has either S1 or S2, it will be rejected by the stigma of the parent plant.

**Hint:** Focus on the fact that the stigma will reject any pollen grain that has the same S alleles as itself.

### Step 3: Analyze the Pollen Grain Genotypes
We need to determine which pollen grain genotypes can successfully fertilize the ovules of the `S1S2` parent. The pollen grains must have neither S1 nor S2 alleles.

**Hint:** Look for pollen grain genotypes that do not include S1 or S2.

### Step 4: Evaluate the Options
Let's assume we have the following options for pollen grain genotypes:
1. S1S1
2. S2S2
3. S3S4
4. S1S2

- **Option 1 (S1S1):** This pollen grain carries S1, which is incompatible with the stigma.
- **Option 2 (S2S2):** This pollen grain carries S2, which is also incompatible with the stigma.
- **Option 3 (S3S4):** This pollen grain carries neither S1 nor S2, making it compatible with the stigma.
- **Option 4 (S1S2):** This pollen grain is identical to the stigma and will be rejected.

**Hint:** Compare each option against the S1 and S2 alleles to determine compatibility.

### Step 5: Conclusion
The only pollen grain genotype that can fertilize the `S1S2` parent is **S3S4**. This is because it does not carry either of the S alleles present in the parent plant.

**Final Answer:** The pollen grains of genotype **S3S4** can fertilize the `S1S2` parent.