Question

Work out a cross between a tall pea plant bearing violet flowers (heterozygous for both) with a dwarf pea plant having white flowers. Write the genotypes and phenotypes of the progeny along with their ratios. Name such a cross and state its importance.

Answer 1

Genotypes of parents:

• • Tall, violet flowered plant (heterozygous for both traits): TtVv
  • Dwarf, white flowered plant (homozygous recessive for both traits): ttvv

Gametes produced by TtVv: TV, Tv, tV, tv

Gametes produced by ttvv: tv (only one type since both recessive alleles are homozygous)

Progeny genotypes and phenotypes:

Progeny Genotype	Phenotype
TtVv	Tall, Violet
Ttvv	Tall, White
ttVv	Dwarf, Violet
ttvv	Dwarf, White

Phenotypic ratio: Tall Violet : Tall White : Dwarf Violet : Dwarf White = 1 : 1 : 1 : 1

Importance of Test Cross: It is used to determine whether an individual showing a dominant phenotype (like tall, violet flowered) is homozygous or heterozygous for the traits. By crossing with a homozygous recessive, the phenotypic ratio of the progeny can reveal the genotype of the parent.