CBSE Class 10 Science 2017 · Paper 31(B)/C · Question 14

Mendel crossed pure-breeding pea plants differing in two traits: one with round, yellow seeds (RRYY) and one with wrinkled, green seeds (rryy). F1: all plants had round, yellow seeds (RrYy), so round and yellow are dominant. F2 (F1 self-pollinated): four kinds of seeds appeared, round yellow, round green, wrinkled yellow and wrinkled green, in the ratio $9:3:3:1$. Round green and wrinkled yellow are new combinations found in neither parent. They appear, $3$ and $3$ in every $16$, because the factor for seed shape and the factor for seed colour go into the gametes independently of each other (gametes RY, Ry, rY and ry in equal numbers); each trait on its own still shows $3:1$. Hence the two traits are inherited independently.