Question

Tallness of pea plants is a dominant trait, while dwarfness is the alternate recessive trait. When a pure-line tall is crossed with pure-line dwarf, what fraction of talI plants in F₂ shall be heterozygous ? Give reasons.

Answer 1

Pull line tall is crossed with pure line Dwarf

Phenotypic ratio  = Tall  :  dwarf  

                                 3    :     1 

Genotypic ratio  =  TT  :   Tt  :  tt  

                                 1  :    2  :  1

Two third of tall progenies are heterozygous because gene for tallness (T) is dominant and also expresses itself in heterozygous condition. 

A Punnet square is used to understand a typical monohybrid cross between tall and dwarf plants.