In a monohybrid cross, we get a genotypic ratio of :

Options

A. `1:2:1`
B. `2:1:2`
C. `0:1:0`
D. `2:1:1`

Answer

To solve the question regarding the genotypic ratio in a monohybrid cross, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Monohybrid Cross**: A monohybrid cross involves the study of inheritance of a single trait. For example, we can consider the trait of plant height, where 'T' represents the dominant allele for tall plants and 't' represents the recessive allele for dwarf plants.

2. **Identify Parental Generation**: In our example, we have two parental plants: one homozygous tall plant (TT) and one homozygous dwarf plant (tt).

3. **Gamete Formation**: The tall plant (TT) can only produce gametes with the allele 'T', while the dwarf plant (tt) can only produce gametes with the allele 't'. Thus, the gametes from the parental generation are:
- From TT: T
- From tt: t

4. **F1 Generation**: When we cross these two parental plants (TT x tt), all offspring in the F1 generation will be heterozygous (Tt) and will exhibit the dominant trait, which is tallness.

5. **Selfing the F1 Generation**: Next, we self-fertilize the F1 generation (Tt x Tt). This will allow us to observe the genotypes of the offspring.

6. **Punnett Square**: We can use a Punnett square to determine the possible genotypes from the selfing of Tt x Tt:
```
T t
----------------
T | TT | Tt |
----------------
t | Tt | tt |
----------------
```

7. **Determine Genotypic Ratio**: From the Punnett square, we can see the resulting genotypes:
- 1 TT (homozygous tall)
- 2 Tt (heterozygous tall)
- 1 tt (homozygous dwarf)

Therefore, the genotypic ratio is 1 TT : 2 Tt : 1 tt, which can be expressed as 1:2:1.

8. **Conclusion**: The genotypic ratio in a monohybrid cross is 1:2:1.

### Final Answer:
The genotypic ratio in a monohybrid cross is **1:2:1**.

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