Explain dihybrid cross with suitable example.

Explanation

(1) A cross which involves two pairs of alleles is called a dihybrid cross. A phenotypic ratio of 9 : 3 : 3 : 1 obtained in the `F_(2)` generation of a dihybrid cross is called a dihybrid ratio.
(2) Thus for example, when we cross a true breeding pea plant bearing yellow and round seeds with a true breeding pea plant bearing green and wrinkled seeds we get pea plants bearing yellow and round seeds in the `F_(1)` generation.
(3) When `F_(1)` plants are selfed, we get a ratio of 9 : 3 : 3 : 1 in the `F_(2)` generation, where 9 plants bear yellow round seeds, 3 plants bear yellow wrinkled seeds, 3 plants bear green round seeds and 1 plant bears green wrinkled seeds.
(4)
Here, the symbol e.g. represents the male gamete while the symbol represents the female gamete.
Yellow round = 9, Yellow wrinkled = 3,
Green round = 3, Green wrinkled = 1,
Phenotypic ratio = 9 : 3 : 3 : 1