The dihybrid cross is a breeding experiment in which two parental organisms that differ in two contrasting traits are crossed. The traits are usually represented by letters, with one letter representing each trait. For example, let's say we are crossing plants that differ in flower color (A = purple, a = white) and seed shape (B = round, b = wrinkled).

When we cross two heterozygous individuals (AaBb x AaBb), we can use a Punnett square to determine the possible genotypes and phenotypes of the offspring. In the F1 generation, all the offspring will be heterozygous for both traits (AaBb).

In the F2 generation, when the F1 individuals are crossed with each other, the genotypes and phenotypes will segregate according to the principles of Mendelian genetics. The Punnett square for the dihybrid cross will have 16 squares, representing the possible combinations of alleles from the gametes of the F1 individuals.

To determine the ratio of the parental genotypes in the F2 generation, we need to identify the possible combinations that result in the parental genotypes. In this case, the parental genotypes are AA BB, AA bb, aa BB, and aa bb.

Let's break down the Punnett square to see how these genotypes can be obtained:
- In 2 of the 16 squares, both alleles for flower color and seed shape will be homozygous dominant (AA BB).
- In 2 of the 16 squares, both alleles for flower color and seed shape will be homozygous recessive (aa bb).
- In 1 of the 16 squares, the alleles for flower color will be homozygous dominant (AA) and the alleles for seed shape will be homozygous recessive (bb).
- In 1 of the 16 squares, the alleles for flower color will be homozygous recessive (aa) and the alleles for seed shape will be homozygous dominant (BB).

Therefore, out of the 16 possible combinations, only 2 will result in the parental genotypes. This gives us a ratio of 2/16, which can be simplified to 1/8.

Therefore, the correct answer is option 'A' (2/16).