Question

(ii) A pure tall plant (TT) is crossed with a pure dwarf plant (tt). Draw Punnett squares to show

(1) F₁ generation

(2) F₂ generation.

(iii) Give the phenotype of the F₂ generation.

(iv) Give the phenotypic and genotypic ratio of the F₁ and F₂ generations.

Answer 1

Part (ii)

A pure tall plant (TT) is crossed with a pure dwarf plant (tt).

Part (1)

For F₁ generation

The gametes produced from the two plants will be: T, T, t, t. For F₁ generation, the Punnett square is as shown below:

Male/ Female	T	T
t	Tt	Tt
t	Tt	Tt

Part (2)

For F₂ generation

The gametes produced from the plants of F₁ generation will be: T, t, T, t. So, when the plants of F₁ generation are self - crossed, for F₂ generation, the Punnett square is as shown below:

Male/ Female	T	t
T	TT	Tt
t	Tt	tt

Part (iii)

As we can see in the above Punnett square, the phenotypes in the F₂ generation are:

(i) Tall plants (TT, Tt)

(ii) Dwarf plants (tt)

There are three tall plants and one dwarf plant. So, the phenotypic ratio of F₂ generation is 3:1.

Part (iv)

For F₁ generation:

Genotypic ratio is 1 (All Tt plants).

Phenotypic ratio is also 1(All tall plants).

For F₂ generation:

Genotypic ratio is TT : Tt : tt = 1 : 2 : 1.

Phenotypic ratio is 3 : 1 (tall : dwarf).