A dwarf pea plant was treated with gibberellic acid. It grows as a pure tall pea plant. If the treated plant is crossed with a pure tall plant, the phenotypic ratio of `"F"_(1)` is likely to:

Options

A. All dwarf
B. All tall
C. `75%` tall and `25%` dwarf
D. `75%` dwarf and `25%` tall

Answer

To solve the question, we need to analyze the genetic background of the dwarf pea plant and the effects of gibberellic acid.

### Step-by-Step Solution:

1. **Identify the Genotypes**:
- The dwarf pea plant has the genotype `tt` (homozygous recessive).
- The pure tall plant has the genotype `TT` (homozygous dominant).

2. **Effect of Gibberellic Acid**:
- The dwarf pea plant is treated with gibberellic acid, which allows it to grow tall. However, this treatment only affects the phenotype, not the genotype. Therefore, the treated dwarf plant is still genetically `tt`, even though it appears tall.

3. **Crossing the Plants**:
- When the treated dwarf plant (`tt`) is crossed with a pure tall plant (`TT`), we can set up a Punnett square to determine the offspring.

4. **Gamete Formation**:
- The gametes from the dwarf plant (`tt`) will be `t` and `t`.
- The gametes from the pure tall plant (`TT`) will be `T` and `T`.

5. **Punnett Square**:
- The possible combinations from the cross are:
- `Tt` (from `T` of tall plant and `t` of dwarf plant)
- `Tt` (from `T` of tall plant and `t` of dwarf plant)
- Therefore, all offspring will be `Tt`.

6. **Phenotypic Ratio**:
- Since all offspring are `Tt`, they will all exhibit the tall phenotype.
- Thus, the phenotypic ratio of the F1 generation will be **100% tall**.

### Conclusion:
The phenotypic ratio of the F1 generation is likely to be **all tall plants**.

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