A pure tall pea plant is crossed with pure dwarf Pea Plant. The progeny is self-pollinated. The ratio of true breeding tall Pea plants to true breeding dwarf Pea plants shall be

Options

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

Answer

To solve the problem of determining the ratio of true breeding tall pea plants to true breeding dwarf pea plants when a pure tall pea plant is crossed with a pure dwarf pea plant, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parental Generation**:
- The pure tall pea plant can be represented as **TT** (homozygous dominant).
- The pure dwarf pea plant can be represented as **tt** (homozygous recessive).

2. **Perform the Cross**:
- When we cross TT (tall) with tt (dwarf), the offspring (F1 generation) will all be heterozygous **Tt**.
- This is because each offspring receives one allele from each parent (T from the tall parent and t from the dwarf parent).

3. **Analyze the F1 Generation**:
- All the progeny in the F1 generation will exhibit the tall phenotype since T (tall) is dominant over t (dwarf).
- Therefore, the phenotype of all F1 plants is tall.

4. **Self-Pollinate the F1 Generation**:
- Now, we self-pollinate the F1 generation (Tt x Tt).
- We can set up a Punnett square to determine the genotypes of the F2 generation.

5. **Punnett Square for F2 Generation**:
- The Punnett square for Tt x Tt will look like this:
```
T t
------------
T | TT | Tt |
------------
t | Tt | tt |
```
- From the Punnett square, we can see the following genotypes:
- 1 TT (homozygous tall)
- 2 Tt (heterozygous tall)
- 1 tt (homozygous dwarf)

6. **Determine the Phenotypic and Genotypic Ratios**:
- The phenotypic ratio of tall to dwarf plants in the F2 generation is 3:1 (3 tall: 1 dwarf).
- The genotypic ratio is 1:2:1 (1 TT: 2 Tt: 1 tt).

7. **Identify True Breeding Plants**:
- True breeding tall plants are those that are homozygous (TT).
- True breeding dwarf plants are those that are homozygous (tt).

8. **Calculate the Ratio of True Breeding Tall to True Breeding Dwarf**:
- In the F2 generation, there is 1 TT (true breeding tall) and 1 tt (true breeding dwarf).
- Therefore, the ratio of true breeding tall pea plants to true breeding dwarf pea plants is **1:1**.

### Final Answer:
The ratio of true breeding tall pea plants to true breeding dwarf pea plants is **1:1**.

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