Question

Explain dihybrid cross.

Answer 1

In a dihybrid cross , two pairs of alleles or contrasting characters are considered in parents.

For example, cotyledon colour and seed shape of pea are used as two pairs of alleles.
Suppose, among the two parents, one was true breeding dominant i.e. yellow coloured cotyledons and round seeds, YYRR and the other was a true breeding recessive i.e. green coloured cotyledons and wrinkled seeds, yyrr. On crossing the two parents, F₁ generation so obtained had all yellow and round seeds.

On self pollinating, the hybrids - YyRr produced four types of seeds in F₂ generation:

(i) Yellow cotyledons and round seeds (YYRR)
(ii) Yellow cotyledons and wrinkled seeds (YYrr)
(iii) Green cotyledons and round seeds (yyRR)
(iv) Green cotyledons and wrinkled seeds (yyrr)

Thus the phenotypic ratio of a dihybrid cross is 9:3:3:1.