Question

You are given axial pea flowers with violet colour whose genotypes are unknown. How would you find the genotype of these plants? Explain with the help of cross.

Answer 1

A test cross is used to determine the genotype of a pea plant with axillary flowers and violet flowers. A homozygous recessive pea plant with terminal flowers and white color is mated with an unknown genotype plant with axial flowers and violet color. The recessive plant has the genotype aa bb.

Assume that the flower’s position is determined by alleles A and a, and its color is determined by alleles B and b. Axial flowers (A) are dominant over terminal flowers (a), and violet flowers (B) are dominant over white flowers (b) on the pea plant. Therefore, the unidentified plant may be heterozygous (AaBb) or homozygous dominant (AABB).

Possible outcomes:

If the unknown plant is homozygous dominant (AABB), only one kind of gamete will be produced by homozygous dominant and homozygous recessive pea plants. Because the dominant alleles will be acquired, all children in the F generation will exhibit axial, violet blooms.

Parents: AABB × aabb

Gametes: AB × ab

	AB
Ab	AaBb (Axial, violet flowers)

If the unknown plant is Aa Bb (heterozygous): The four types of gametes that the heterozygous dominant pea plant will produce are AB, Ab, aB, and ab. For axial, violet flowers, axial, white flowers, terminal, violet flowers, and terminal, white flowers, the progeny will exhibit a 1 : 1 : 1 : 1 phenotypic ratio.

Parents: AaBb × aabb

	AB	Ab	aB	ab
ab	AaBb (Axial, violet flowers)	Aabb (Axial, white flowers)	aaBb (Terminal, violet flowers)	aabb (Terminal, white flowers)