Dihybrid Cross Genotypic Ratio

Dihybrid Cross:

After establishing the law of segregation from the study of monohybrid crosses, Mendel conducted experiments to study the segregation and inheritance of two pairs of contrasting characters simultaneously. He studied the inheritance of yellow and green colors of seeds along with the round and wrinkled character of the seed coats.

Mendel found that a cross between yellow, round and green, wrinkled seeds (Parent Generation) produced only yellow and round seeds in F1 generation. In F2 generation four combinations of these characters appeared in the following ratio:

i. Yellow Round         9         Parental combination

ii. Yellow Wrinkled      3         Nonparental combination

iii. Green Round           3         Parental combination

iv. Green Wrinkled      1         Parental combination

Thus, the offspring of F2 generation was produced in a 9 : 3 : 3 : 1 ratio. This is called the Dihybrid ratio. The two of these combinations were similar to the parents while the other two were new.