Explain Dihybrid cross in pea plant .

Explanation

The crossing of two plants differing in two pairs of contrasting traits is called dihybrid cross.
(ii) Mendel considered the seed shape (round and wrinkled) and cotyledon colour (yellow & green) as the two characters.
(iii) In seed shape round (R ) is dominant yellow wrinkled (r ) , in cotyledon colour yellow (Y) is dominant over green (y).
(iv) Hence the pure breeding round yellow parent is represented by the genotype RRYY and the pure breeding green wrinkled parent is represented by the genotype rryy.
(v) During gamete formation the paired genes of a character assort out independently of the other pair.
(vi) The resultant gametes thus will be genetically different and they are of the following four types :

These four types of gametes of `F_(1)` dihybrids unite randomly in the process of fertilization and produce sixteen types of individuals in `F_(2)` in the ratio of `9 : 3 : 3 : 1`