Question

Mendel self-pollinated the F2 plants and found that dwarf F2 plants continued to generate dwarf plants in F3 and F4 generations. What do you think he would have got had he self-pollinated a tall F2 plant?

Answer 1

Mendel experiment:

1. When Mendel crossed two varieties of a character (such as tall and short) in pea plants, only the dominant trait (tall) appeared in the F1 generation.
2. The genetic constitution of F1 plants was Tt.
3. In F₁ generation, only hybrid tall plants with genotype Tt were produced.

F2 generation:

1. When heterozygous tall (Tt) plants are self-pollinated, the progeny produced will be both tall and dwarf plants in the ratio of 3:1 in the F2 generation.
2. One tall (homozygous) plant, two tall (heterozygous), and one dwarf plant (tt) are generated.
3. For TT (tall), Tt (tall), and tt (tall), the genotype ratio is 1:2:1. (dwarf).

F3 & F4 generation :

1. Case 1: When we self-pollinate the dwarf plants (tt), only dwarf plants will be produced.
2. Case 2: When we made a cross between hybrid tall plant (Tt) and dwarf plant (tt), it will result in both hybrid tall and dwarf plant in the ratio of 1:1.
3. Case 3: Only tall plants will be produced if we self-pollinate the hybrid tall plant (Tt) and the pure tall plant (TT).
4. Therefore, we can say that the phenotypic ratio depends on the genotype of tall plants.
5. If self-pollinated by hybrid tall plants, dwarf F2 plants continued to produce dwarf plants in F3 and F4 generations (Tt).