According to Mendel, genes have no influence on each other when it comes to the grouping of alleles into gametes. Different features for the same attributes in their offspring are the consequence of a dihybrid cross, which is a cross between two purebred parents. This is a good example of how genes may be arranged in a variety of ways. Note the differences in seed color and texture between two pea plants, one with green, wrinkled seeds (yyrr) and the other with yellow, spherical seeds (yyrr) (YYRR). For homozygous parents, the green/wrinkled plant has all YR sperm, while the yellow/round plant has all YR sperm, according to the segregation criteria. There are no F1 children who are not YyRr genetically. (Golubovskaya,1979)

In order to comply with the law of segregation, F2 generation gametes must have either a R or a r allele, as well as either Y alleles or Ys. When a gamete carries the R allele, the law of independent assortment states that it has the same chance of carrying a R as it does of carrying an R. Because of this, crossing the YyRr heterozygote with itself will result in four equally likely gametes: YR, R, yR, and R. Self-crossing will result in the four following equally likely gametes: All of the letters are in capitals. Every one of the 16 genotypic combinations that can be created by stacking these gametes in a 4 4 Punnett square has an equal chance of occurring. This collection of genotypes includes nine round/yellow genotypes, three-round/green genotypes, three wrinkled/yellow genotypes, and one wrinkled/green genotype. 

Due to distinct assortment and dominance in each monohybrid cross, the phenotypic ratio of 9:3:3:1 dihybrid can be split down into two 3:1 ratios, each of which follows a dominant and recessive pattern. Without considering seed color at all, it is plausible to assume that three-quarters of the F2 generation progeny will be round, with the remaining quarter wrinkled in shape. Three-quarters of the yellow seedlings and one-quarter of the green seedlings are expected to come from the F2 generation. We can apply the product rule to sorting alleles for texture and color because they are separate occurrences. Consequently, the number of spherical and yellow F2 offspring will be (3/4) (3/4) = 9/16, and the number of such offspring will be (1/4) (1/4) = 1/16. It doesn't matter if you use a Punnett square or not. When a parent has one dominant and one recessive trait, the product rule can be used to calculate the number of round/green and wrinkled/yellow children they produce. In this case, the fraction of each is (3/4) / (1/4). (Bennett, 1977)

 

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