Explain "the law of independent assortment'' with a suitable example.

Explanation

Statement of law : When the two homozygous parents differing in two pairs of contrasting traits are crossed the inheritance of one pair is independent of the other. In other words, when a dihybrid (or polyhybrid) forms, Gametes assortment of alleles of different trait is independent of their original combination in the parents. Explanation :
(i) Mendel crossed homozygous pea plant having yellow round seeds (YYRR) with a plant having green wrinkled seeds (yyrr).
(ii) The plants of `F_(1)` are heterozygous for both the characters with the genotype Yr. Rr.
(iii) The `F_(1)` hybrid allowed to self-pollinate.
(iv) The four types of alleles are assorted indepen- dently to produce four types of gametes i.e., YR, Yr, yR,yr.
(v) First the genes Y, y, R, r separate and then the gamete which receives Y or y gene for colour may receive R or r for shape of seed and forms total four types of gametes e.g., Gene Y may combine with R or r, in the same way y combines with R or r.
(vi) Thus, the four types of gametes unite at random and produce 16 types of individuals of `F_(2)` generation.
(vii) In additional to parental combination yellow round and green wrinkled, two new combinations as yellow wrinkled and gteen round are produced.

(viii) The appearance of new combination in `F_(2)` generation proved the law of independent assortment.
(ix) They showed that each pair of contrasting character behaves independently and have no permanent association with particular character.
(x) The 16 individuals produced in `F_(2)` generation are in 9 : 3 : 3 : 1 ratio, 9 yellow round, 3 yellow wrinkled, 3 green round, and 1 green wrinkled.