Question

In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F₂ is

• A. 1:3
• B. 1:1
• C. 1:2
• D. 2:1

Answer 1

The correct option is B

1:1

The correct option is B.

Explanation of the correct option:

1. When a pure tall plant (TT) is crossed with the pure short plant (tt), then the progeny in the F₁ generation will be hybrid (Tt).
2. When the F₁ generation is self-crossed (Tt), then in the F₂ generation, the progeny produced will be tall homozygous (TT), Tall heterozygous (Tt), and dwarf homozygous in the ratio of 1:2:1.
3. This type of cross between single pair of contrasting characters is called a monohybrid cross.
4. The tall and dwarf plants were produced in a ratio of 3:1 (75% tall plants and 25% dwarf plants).
5. But in the given question, the ratio of pure tall plants to short plants in F₂ will be 1:1.

Explanation of the incorrect options:

Option A:

1. A pure tall (TT)plant is crossed with a pure short (tt) plant.
2. The first generation will be tall (Tt) and it is a hybrid plant.
3. When Tt x Tt is crossed next generation will be TT, Tt, Tt, tt.
4. 3 tall and 1 short plant in the second generation are found.

Option C:

1. When a pure tall plant (TT) is crossed with the pure short plant (tt), then the progeny in the F₁ generation will be hybrid (Tt).
2. When the F₁ generation is self-crossed (Tt), then in the F₂ generation, the progeny produced will be tall homozygous (TT), Tall heterozygous (Tt), and dwarf homozygous in the ratio of 1:2:1.

Option D:

1. When a pure tall (TT)plant is crossed with a pure short (tt) plant. The first generation will be tall (Tt) and it is a hybrid plant.
2. When Tt x Tt is self-crossed next generation produced will be TT, Tt, Tt, and tt in the ratio of 1:2:1, in which there are 1 pure tall, 2 hybrids, and 1 short plant.

Final answer: The ratio of pure tall plants to short plants in F₂ is 1:1.