In a case of incomplete dominance, true breeding red flowerd plant (RR) is crossed with true breeding white flowered plant (rr). What would be correct `F_(2)` ratio ?

Options

A. 1 red : 2 pink : 1 white
B. 3 red : 1 white
C. 1 red : 1 pink : 2 white
D. 2 red : 1 pink : 1 white

Answer

To solve the problem of determining the F2 ratio in a case of incomplete dominance when a true breeding red flowered plant (RR) is crossed with a true breeding white flowered plant (rr), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parental Genotypes**:
- The true breeding red flowered plant has the genotype RR.
- The true breeding white flowered plant has the genotype rr.

2. **Perform the F1 Cross**:
- When RR is crossed with rr, all F1 offspring will have the genotype Rr.
- In incomplete dominance, the phenotype of the F1 generation is a blend of the two parental phenotypes. Therefore, the F1 plants will have pink flowers.

3. **Self-Cross the F1 Generation**:
- Now, we will self-cross the F1 generation (Rr x Rr) to produce the F2 generation.
- We can use a Punnett square to visualize this cross.

4. **Construct the Punnett Square**:
- The Punnett square for Rr x Rr would look like this:

```
R r
------------
R | RR | Rr |
|-------|------|
r | Rr | rr |
```

5. **Determine the Genotypic Ratio**:
- From the Punnett square, we can see the genotypes of the offspring:
- 1 RR (red)
- 2 Rr (pink)
- 1 rr (white)
- Therefore, the genotypic ratio is 1 RR : 2 Rr : 1 rr.

6. **Determine the Phenotypic Ratio**:
- The phenotypes corresponding to the genotypes are:
- RR = Red flowers
- Rr = Pink flowers
- rr = White flowers
- Thus, the phenotypic ratio is:
- 1 Red : 2 Pink : 1 White.

### Final Answer:
The correct F2 ratio in this case of incomplete dominance is **1 Red : 2 Pink : 1 White**.