Question

What do you understand by Monohybrid and Dihybrid cross? Describe in detail with example.

Answer 1

Monohybrid cross is a cross between two individuals that differ in only one observed trait. Dihybrid cross is a cross between two individuals that differ in two observed traits. In monohybrid cross if a cross is made between homozygous parents having round seed (RR) and wrinkled seed (rr) , the F${}_1$ generation will show progeny will round seed (Rr). If the F${}_1$ generation is self fertilized, the offsprings will show round seed and wrinkled seeds in the ratio of 3:1. The genotypic ratio of F${}_2$ will be 1 (RR):2 (Rr):1 (rr).

In dihybrid cross if a cross is made between homozygous parents showing two contrasting characters, that is plant with round and yellow seeds (RRYY) and plant with wrinkled and green seeds (rryy), the F${}_1$ generation will show all progeny with round and yellow seeds (RrYy). If the F${}_1$ generation is self fertilized, the offsprings will show phenotype in the ratio of 9:3:3:1 where 9 parts will be round and yellow seeds, 3 parts will be round and green seeds, 3 parts will be wrinkled and green seeds and 1 part will be wrinkled and green seeds.