Phenotypic ratio of a monohybrid `F_(2)` progeny of incomplete dominance is

Options

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

Answer

To determine the phenotypic ratio of a monohybrid F2 progeny exhibiting incomplete dominance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Incomplete Dominance**: In incomplete dominance, the phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes. For example, in the case of the plant Mirabilis jalapa, red flowers (RR) and white flowers (rr) produce pink flowers (Rr) in the F1 generation.

2. **Identify Parental Genotypes**: The parental plants are:
- Red flower (homozygous dominant): RR
- White flower (homozygous recessive): rr

3. **Cross the Parents to Get F1 Generation**:
- When RR is crossed with rr, all offspring (F1) will be heterozygous (Rr), resulting in pink flowers.

4. **Selfing the F1 Generation**:
- Now, we will self-cross the F1 generation (Rr x Rr).
- The gametes produced by each parent will be R and r.

5. **Construct a Punnett Square**:
- Set up a Punnett square to determine the F2 generation:
```
R r
------------
R | RR | Rr |
------------
r | Rr | rr |
```

6. **Analyze the F2 Generation**:
- The resulting genotypes from the Punnett square are:
- 1 RR (red)
- 2 Rr (pink)
- 1 rr (white)

7. **Determine the Phenotypic Ratio**:
- The phenotypes corresponding to these genotypes are:
- 1 red (RR)
- 2 pink (Rr)
- 1 white (rr)
- Therefore, the phenotypic ratio is 1 red : 2 pink : 1 white.

8. **Final Answer**:
- The phenotypic ratio of the F2 progeny in the case of incomplete dominance is **1:2:1**.