There are different types of genotypes that can be observed in the F2 generation of a dihybrid cross. These genotypes are determined by the combination of alleles inherited from the parental generation.

In a dihybrid cross, two traits are being studied simultaneously. Each trait is controlled by two alleles, one inherited from each parent. In the parental generation (P generation), the two parents have different genotypes for each trait. When these parents are crossed, their offspring in the F1 generation will have a heterozygous genotype for both traits.

To determine the genotypes in the F2 generation, we need to consider the possible combinations of alleles that can be inherited from the F1 generation. Each parent in the F1 generation can produce four types of gametes, with two possible alleles for each trait. When these gametes combine, they can produce a total of 16 different genotypes in the F2 generation.

However, not all of these genotypes will be observed in the F2 generation. Some genotypes may be more common than others due to the principles of Mendelian genetics. The distribution of genotypes in the F2 generation can be determined using a Punnett square.

In a dihybrid cross, the genotypic ratio in the F2 generation is typically 1:2:1:2:4:2:1:2:1. This means that there are nine different genotypes that can be observed in the F2 generation. These genotypes are determined by the combination of alleles from both traits.

The correct answer is option 'D', which states that there are nine types of genotypes in the F2 generation of a dihybrid cross.