In a perfect world, reciprocal classes would be equally represented since they result from the same meiotic event. It is likely that your data suggests the parental classes are NOT equal.

What causes this phenomenon to occur? (Think about the phenotype of each.)

Regarding the genotype and phenotype of the original parents they are known by the name of parental classes. These parental classes have appeared of the genotype are classified as homozygous or heterozygous.

Explanation:

While the reciprocal classes are also the genotypes and phenotypes of the crosses. These reciprocal classes are personified if the crossing occurs between the homozygous alleles. This is due to the fact that the chromosomal part is exchanged in the two chromosomes, since the cross products are the same as the products that are formed in the parent classes, this occurs in a phenomenon known as homozygosity.

In the event that the crossover occurs in a heterozygous allelic tetrad, then an exchange between the different chromosomal parts will occur, resulting in recombinant alleles. In this particular case, the parenting classes cannot be the same. This phenomenon is known as heterozygosity.