Question

A homozygous tall plant (T) bearing red coloured(R) flowers is crossed with a homozygous dwarf(t) plant bearing white(r) flowers. What is the phenotypic ratio obtained in F2 generation?

Answer 1

Hint: A cross between two identical hybrids considering the two phenotypic traits is known as a dihybrid cross. This type of cross was first demonstrated by Mendel in a pea plant. The purpose of a dihybrid cross is to establish relationships between the different allelic pairs.

Complete Answer:
To solve this question, we must know about the dihybrid cross.
According to the question, the cross is made between a homozygous tall plant (T) bearing red coloured(R) flowers and crossed with a homozygous dwarf(t) plant bearing white(r) flowers. The gene is expressed as TTRR X ttrr.
The F1 generation is TtRr.
The F2 generation is the cross between F1 offsprings.
The gametes produced are -TR, Tr, tR, tr

	TR	Tr	tR	tr
TR	TTRR (Tall, red)	TTRr(Tall, red)	TtRR(Tall, red)	TtRr(Tall red)
Tr	TTRr(Tall, red)	TTrr(Tall,white)	TtRr(Tall, red)	Ttrr (Tall,white)
tR	TtRR(Tall,red)	TtRr(Tall,red)	ttRR(dwarf, red)	ttRr(dwarf, red)
tr	TtRr(Tall, red)	Ttrr(Tall,white)	ttRr(dwarf, red)	ttrr(dwarf,white)

The phenotypic ratio of the F2 generation is Tall, red- 9, Tall white-3, dwarf red-3, dwarf white-1.
So the ratio is 9:3:3:1

Note: Based on the results of the dihybrid cross, Mendel put forward the theories that is law of independent assortment, law of dominance and law of segregation. Law of dominance states that in a heterozygote, the trait which is expressed is called the dominant trait and the one that is not is the recessive trait.