Question

A cross was performed between tall and dwarf plants.
If the phenotypic ratio obtained in the progeny is 1 : 1. Determine the genotype of tall parent

• A. TT
• B. Tt
• C. tt
• D. Difficult to predict

Answer 1

The correct option is B Tt

Tall trait is dominant over the dwarf trait in pea plants.

Let 'T' and 't' be the alleles responsible for tallness and dwarfness respectively.

Hence, the tall plant can be of two different genotypes:
TT (homozygous) or Tt (heterozygous).

When a tall plant is crossed with a dwarf plant (tt) and the progeny obtained show tall and dwarf traits in the ratio of 1 : 1, then the genotype of the tall parent is heterozygous (Tt) .


$F_1$ phenotypic ratio= Tall : dwarf = 1 : 1

When a tall plant is crossed with a dwarf plant (tt) and all the offspring show dominant phenotype i.e. tall trait, then the genotype of the tall parent is homozygous (TT).


$F_1$ phenotype: 100% offspring are of tall phenotype.

As given in the question, the ratio between tall and dwarf plants in the offspring is 1 : 1, hence, the genotype of the tall plant is Tt.