Ans.

Experiment – Mendel selected two types of pea plants for a dihybrid cross.  The seed of the first variety was round and the cotyledon was yellow in color (RRYY).  The seed of the second variety was wrinkled and the cotyledon was green (rryy). round The shape of the seed is round and the yellowness of the cotyledon is the dominant characteristic.  He crossed both types of plants and got the first generation (F) plant, whose seeds were round and cotyledons were yellow in color.

 RRYY × rryy → RrYy F, – generation

 (round seeds and yellow cotyles elf-pollination F1 generation plant by self-pollination in the first generation (F2) plant.  There were four types of gametes in these plants- (a) Round-yellow (RY) (b) Round-green (Ry) (c) Wrinkled yellow (rY) (d) Winkled green (ry) and they’re the aratio9  : 3 : 3: 1 was.

Round-yellow (RRYY) × Wrinkled-green (rryy) ………P generation

↓

Round-yellow (RrYy). …………..F1 generation(Hybrid)

                                                                            ↓

Round-yellow (RrYy) × Round-yellow (RrYy)……. F1 plants

                                                                           ↓

(a) Round-yellow (RY) (b) Round-hura (Ry) (c) Wrinkled-yellow (rY) (d) Wrinkled-green (ry). , 

↓

Gametes

This ratio is clear from the following checker-board

(Checker Board of dihybrid cof)

Phenotypic ratio=9:3:3:1

Genotypic ratio=1:2:2:4:1:2:,1:2:1

Conclusion – From the dihybrid cross, Mendel concluded that the factors of genetic traits (now called genes) are mutually independent.  This is the reason that in the second generation (F2) of dihybrid hybridization the yellow color is freely associated not only with round seeds but also with wrinkled seeds.  Similarly, green color also appears not only with wrinkled seeds but also with round seeds.  From this cross, Mendel derived the ‘law of independent assortment

Principle of independent mating – When the factors of two opposing traits participate in a cross, then both the pairs are completely independent of each other at the time of segregation and gamete formation, and these factors  ) can produce new properties by combining with other factors of different traits.  This rule arises from a dihybrid cross.