Question

One student (researcher) wants to cross pure tall plant (TT) with pure dwarf (tt) plant, what would be the Fj and F2 generations? Explain.

Answer 1

1. Pure tall plant has both the factors of the same type ‘TT’. 

2. Pure dwarf plant has both the factors of the same type ‘tt’. 

3. When a pure tall plant (TT) is crossed with pure dwarf plant (tt), all the offsprings in Fj generation are tall (Tt). 

4. So all the plants are heterozygous tall, as ‘T’ is the dominating factor.

5. On self pollination of these F₁ generation plants the new breed can have any combination of T and t like TT, Tt, Tt or tt.

6. So in F₂ generation 75% of plants are tall and 25% of plants are dwarf. Thus the phenotype ratio is 3 : 1. 

7. Among 75% of tall plants 25% are pure tall (TT) or homozygous tall, remaining 50% are heterozygous tall (Tt, tT). 

8. The remaining 25% dwarf plants are pure or homozygous dwarf (tt). 9. So the genotype ratio is 1 : 2 : 1.