When a red floweered plant was cross pollinated by white flowered one and the offspring were self pollinated to obtain a phenotypic ratio of `1:2:1` it has to be a case of :-

Options

A. Incomplete dominince
B. Dominance
C. Recessive epistasis
D. Pleurotropic effect of genes

Answer

To solve the question regarding the phenotypic ratio of `1:2:1` resulting from the cross-pollination of a red flowered plant with a white flowered plant, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Cross**:
- We have a red flowered plant (let's denote it as R) and a white flowered plant (denote it as r). The red flower is dominant over the white flower.

2. **Determine the Genotypes**:
- The red flowered plant can be either homozygous (RR) or heterozygous (Rr). The white flowered plant must be homozygous recessive (rr).

3. **Perform the Cross**:
- If we assume the red flowered plant is heterozygous (Rr), the cross would be Rr (red) x rr (white).

4. **Use a Punnett Square**:
- Set up a Punnett square to determine the offspring:
```
R r
---------
r | Rr | rr |
---------
r | Rr | rr |
---------
```
- The offspring genotypes will be:
- Rr (red flower) - 2 occurrences
- rr (white flower) - 2 occurrences

5. **Calculate the Phenotypic Ratio**:
- The phenotypic ratio from this cross will be:
- Red flowers (Rr): 2
- White flowers (rr): 2
- This gives us a phenotypic ratio of 2:2, which simplifies to 1:1.

6. **Self-Pollination of Offspring**:
- If the offspring (Rr and rr) are self-pollinated, we can analyze the next generation:
- Rr x Rr will yield:
```
R r
---------
R | RR | Rr |
---------
r | Rr | rr |
---------
```
- The genotypes will be:
- RR (red): 1
- Rr (red): 2
- rr (white): 1
- This gives a phenotypic ratio of 3 red: 1 white.

7. **Identify the Type of Inheritance**:
- The phenotypic ratio of 1:2:1 indicates that this is a case of **incomplete dominance**. Incomplete dominance occurs when neither allele is completely dominant, resulting in a blending of traits.

### Conclusion:
The correct answer to the question is that the case described is **incomplete dominance**.

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