A dihybrid cross is a breeding experiment which is done between organisms that differ in two traits. Dihybrid cross was invented by Mendel to study if different traits of pea, like seed shape and flower color were inherited independently. Based on this he proposed that alleles of different genes are assorted independently during the formation of gametes.
Based on his experiments on pea plants Mendel summarized his finding as Law of segregation (Mendelâ€™s first law) and Law if independent assortment (Mendel's second law).
Mendelâ€™s dihybrid cross can be calculated using Punnett square and by tree method. The potential genetic makeup of the offspring of a particular cross can be shown using Punnett square. The Punnett square is useful to determine probabilities of phenotype and genotype ratios in the offspring.
For example a cross between round, yellow and wrinkled green pea seeds produced only round yellow pea seeds in the first filial generation (F1 generation), but in the second filial generation (F2 generation) 4 different types of combinations appeared of which two differed from that of the parental combinations. The genotype of the F1 generation is RrYy and of F2 generation is RRYY, RRYy, RrYY, RrYy, RRYy, RRyy, RrYy, Rryy, RrYY, RrYy, rrYY, rrYy, RrYy, Rryy, rrYy, and rryy. The offspringâ€™s of the F2 generation were produced in a ratio of 9:3:3:1 and this ratio is known as dihybrid ratio. Please refer: dihybrid cross