In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in `F_(2)` is

Options

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

Explanation

To solve the problem of determining the ratio of pure tall plants to short plants in the F2 generation after crossing a pure tall plant (TT) with a short plant (tt), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parent Plants**:
- The pure tall plant has the genotype **TT** (homozygous dominant).
- The short plant has the genotype **tt** (homozygous recessive).

2. **Cross the Parent Plants**:
- When we cross TT (tall) with tt (short), we can determine the genotype of the F1 generation.
- The gametes from the tall plant (TT) can only be T, and the gametes from the short plant (tt) can only be t.
- Therefore, the F1 generation will all be **Tt** (heterozygous).

3. **Phenotype of F1 Generation**:
- All plants in the F1 generation (Tt) will exhibit the tall phenotype because T (tall) is dominant over t (short).

4. **Self-Pollinate F1 Generation**:
- To find the F2 generation, we self-pollinate the F1 plants (Tt x Tt).
- We can set up a Punnett square to visualize the possible combinations of alleles.

5. **Construct the Punnett Square**:
- The Punnett square for Tt x Tt will look like this:

| | T | t |
|-----|-----|-----|
| **T** | TT | Tt |
| **t** | Tt | tt |

6. **Determine the Genotypes of F2 Generation**:
- From the Punnett square, we see the following genotypes:
- 1 TT (homozygous tall)
- 2 Tt (heterozygous tall)
- 1 tt (homozygous short)

7. **Count the Phenotypes**:
- The phenotypes can be counted as follows:
- Tall plants: TT + Tt + Tt = 3 tall plants
- Short plants: tt = 1 short plant

8. **Calculate the Ratio**:
- The ratio of tall plants to short plants in the F2 generation is therefore **3:1**.

### Final Answer:
The ratio of pure tall plants to short plants in the F2 generation is **3:1**.

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