In pea, a pure tall plant (TT) is crossed with a short plant (tt). What will be the ratio of pure tall plants to short plants in the F₂ generation ?
1:1
1:3
3:1
2:1
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC CDS-2 – 2021
Parental Generation (P): TT x tt
The gametes produced by the TT parent are all T. The gametes produced by the tt parent are all t.
First Filial Generation (F1): When TT is crossed with tt, the offspring (F1) are all heterozygous tall (Tt).
F1 selfing: Tt x Tt
The gametes produced by a Tt plant are T and t, in equal proportions (1:1).
To find the F2 generation, we cross the F1 gametes:
Punnett Square:
| T | t
—|—-|—-
T | TT | Tt
t | Tt | tt
The genotypes in the F2 generation are TT, Tt, and tt in the ratio 1:2:1.
The phenotypes are Tall (TT and Tt) and Short (tt).
The ratio of Tall to Short phenotypes is 3:1.
The question asks for the ratio of **pure tall plants (TT)** to **short plants (tt)** in the F2 generation.
From the genotype ratio (1 TT : 2 Tt : 1 tt), the number of pure tall plants (TT) is 1 unit, and the number of short plants (tt) is 1 unit.
Therefore, the ratio of pure tall plants to short plants in the F2 generation is 1:1.
– F1 generation from TT x tt is always Tt (heterozygous tall).
– F2 generation from Tt x Tt has genotypes TT, Tt, tt in ratio 1:2:1.
– Pure tall is TT, short is tt.