In case of co-dominance the monohybrid ratio of phenotypes in `F_(2)` generation is :-

Options

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

Answer

To solve the question regarding the monohybrid ratio of phenotypes in the F2 generation under co-dominance, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Co-dominance**: Co-dominance occurs when both alleles in a heterozygote are fully expressed, resulting in a phenotype that is neither dominant nor recessive. An example is the crossing of red and white flowers, where the offspring exhibit a blend of both colors.

2. **Define the Alleles**: Let's denote the alleles for flower color as follows:
- Capital R (R) for red color
- Small r (r) for white color

3. **Parental Generation (P)**: When we cross a homozygous red flower (RR) with a homozygous white flower (rr), the parental generation can be represented as:
- RR (red) x rr (white)

4. **F1 Generation**: The offspring from this cross will all be heterozygous (Rr) and will display the co-dominant phenotype. In this case, the phenotype will be pink (not red or white), as both alleles contribute to the phenotype.

5. **F2 Generation**: To find the F2 generation, we need to cross the F1 generation (Rr x Rr):
- The possible gametes from each Rr parent are R and r.
- The Punnett square for this cross will look like this:

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

6. **Phenotypic Ratio**: From the Punnett square, we can see the resulting genotypes:
- 1 RR (red)
- 2 Rr (pink)
- 1 rr (white)

Therefore, the phenotypic ratio in the F2 generation is:
- 1 red : 2 pink : 1 white

7. **Conclusion**: The correct answer for the monohybrid ratio of phenotypes in the F2 generation under co-dominance is **1:2:1**.

### Final Answer:
The monohybrid ratio of phenotypes in the F2 generation in case of co-dominance is **1:2:1** (Option B).