Dihybrid and Dihybrid Cross.

After thoroughly studying each trait separately, Mendel decided to study the inheritance of two simultaneously, e.g., seed shape and seed colour.

Traits.

Seed shape could be round or wrinkled. Similarly, seed colour could be yellow or green. Parents.. He crossed true breeding round and yellow seed plants with true breeding wrinkled and green seed plants.

F1 Offsprings.

All F1 dihybrid were round and yellow seeded due to dominance. Self-fertilization. Then he made a dihybrid cross by allowing self-fertilization among F1 dihybrids. The results was quite surprising.

F2 Generation.

Seeds produced as F2 progeny were not only in the

 two parental combination i.e., round yellow and wrinkled green, but also in  Two new phenotypic combination i.e., round green and wrinkled yellow. Ratio. A clear cut 9:3:3:1 phenotypic ratio was found in F2.

Shuffling indication.

Appearance of these new recombinant phenotypes of F2 indicated that some sort of shuffling of alleles had occurred during gametes formation. Mendel interpretations. Mendel inferred the mechanism of this shuffling as independent assortment of alleles into gametes. He concluded that ―the alleles for seed shape and colour were not bound to remain in parental combination forever,‖ i.e. ‗R‘ with ‗Y‘ and ‗r‘ with ‗y‘; rather these were free to assort independently. R could go with Y or y in any gamete with equal change.

Law of Independent Assortment :

Mendel formulated Law of Independent Assortment: “

When two contrasting pairs of traits are followed in the same cross, their alleles assort independently into gametes.‖ i.e. Alleles of one pair inherit independently of alleles of the other pair. The distribution of alleles of one trait into gametes has no influence on the distribution of alleles of the other trait. Thus the chance for a plant to be round or wrinkled is independent of its chance of being yellow or green.