LAW OF INDEPENDENT ASSORTMENT
It states that, when two contrasting pairs of trait are followed in the same cross, their alleles assort independently into the two gametes and the distribution of alleles of one trait into gametes has no influence on the distribution of alleles of the other trait. Alleles of one pair inherit independently of alleles the other pair. Thus the chance for a plant to be rounded or wrinkled is independent of its chance of being yellow or green.
Proof of Law of Independent assortment by Dthybrid Cross
Mendel studied each trait separately. He then decided to study the inheritance of two traits. Thus he used seed shape and seed colour. Seed shape could be round or wrinkled. Similarly, seed colour could be yellow or green.
Cross between green pod tall and yellow
- F1 cross: Mendel crossed true breeding green pod and tall plants with yellow pod and small plants. All the F1 dihybrids were green tall. So green tall is dominant over yellow small.
- F2 cross: Then he self-fertilized the F1 dihybrids. The result was quite different. The F, progeny gives 9:3:3 1 phenotypic ratio. plants produced two types of F2 progeny:
(a) The two parental combinations, i.e., green pod tall and yellow pod small.
(b) Two new phenotypic combinations, i.e green small and yellow pod small.
(b) Cross between Tall purple flower and small
True breed tall plant with purple flower was crossed with small plant with white flower. All were tall purple in F1. In F,, they gave ratios as 9 (tall purple): 3 (tall white): 3 (snpall purple): 1 (small white)