What is the ratio of homozygous genotypes of flower colour in `F_(2)` generation for snapdragon ?

Options

A. `1:1`
B. `2:1`
C. `1:2`
D. `3:1`

Answer

To determine the ratio of homozygous genotypes of flower color in the F2 generation for snapdragon (Antirhinum), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Alleles**: In snapdragons, flower color is determined by two alleles:
- **R** (dominant allele for red color)
- **r** (recessive allele for white color)

2. **Identify the Incomplete Dominance**: In snapdragons, the inheritance of flower color exhibits incomplete dominance. This means that:
- Homozygous dominant (RR) results in red flowers.
- Homozygous recessive (rr) results in white flowers.
- Heterozygous (Rr) results in pink flowers.

3. **Crossing the Parental Generation**:
- When we cross a pure red flower (RR) with a pure white flower (rr), all offspring in the F1 generation will be heterozygous (Rr) and display the pink phenotype.

4. **F1 Generation Self-Cross**:
- Now, if we self-cross the F1 generation (Rr × Rr), we can determine the genotypes of the F2 generation.

5. **Using a Punnett Square**:
- Set up a Punnett square for the cross Rr × Rr:
```
R | r
----------------
R | RR | Rr
----------------
r | Rr | rr
```
- From the Punnett square, we can see the resulting genotypes:
- 1 RR (homozygous dominant)
- 2 Rr (heterozygous)
- 1 rr (homozygous recessive)

6. **Count the Homozygous Genotypes**:
- In the F2 generation, we have:
- 1 homozygous dominant (RR)
- 1 homozygous recessive (rr)
- Therefore, the total number of homozygous genotypes is 2 (1 RR + 1 rr).

7. **Calculate the Ratio**:
- The ratio of homozygous genotypes (RR:rr) in the F2 generation is 1:1.

### Final Answer:
The ratio of homozygous genotypes of flower color in the F2 generation for snapdragon is **1:1**.

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