Dihybrid cross involves the inheritance of two pairs of contrasting characteristics (or contrasting traits) at the same time.The two pairs of contrasting characteristics chosen by Mendel were shape and colour of seeds round -yellow seeds and wrinkled-green seeds .
(i)Mendel first crossed pure breeding pea plants having round-yellow seeds with pure breeding pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the first generation`(F_(1))`.
(ii)From this it was concluded,that round shape and yellow colour of the seeds were dominant traits over the wrinkled shapeand green colour of the seeds.
(iii)When the hybrids of `F_(1)` generation pea plants having round-yellow seeds were cross-bred by self pollination,then four types of seeds having different combinations of shape and colour were obtained in second generation of `F_(2)` generation.They were round yellow, round-green,wrinkled yellow and wrinkled-green seeds.
(iv)The ratio of each phenotype (or appearance) of seeds in the `F_(2)` generation is `9:3:3:1` .This is known as the Dihybrid ratio.
(v)From the above results it can be concluded that the factors for each character or trait identity in the gamete.The factors are idependent to each other and pass to the offsprings (through gametes).
Resuls of a Dihybrid Cross:Mendel got the following results from his dihybrid cross:
(i)Four type of plants:A dihybrid cross produced four of `F_(2)` offsprings in the ratio of 9 with two dominanat traits,3 with one dominant trait and one recessive trait, 3 with another dominant ttrait and another recessive trait and 1 with two recessive traits.
(ii) New combination:Two new combinations of traits with round green and wrinkled yellow had appeared in the dihybrid cross (`F_(2) `generation).
Difference between monohybrid and dihybrid cross:
