Introduction:
A dihybrid cross is a genetic cross involving two pairs of alleles. Incomplete dominance is a type of inheritance pattern in which the heterozygous phenotype is intermediate between the two homozygous phenotypes. In the case of a dihybrid cross involving incomplete dominance, the genotypic ratio may differ from the expected ratio.

Genotypic Ratio:
The genotypic ratio is the ratio of the different genotypes that result from a genetic cross. In a dihybrid cross, the expected genotypic ratio is 9:3:3:1, which means that there are nine possible genotypes resulting from the cross. However, when one pair of alleles shows incomplete dominance, the genotypic ratio may come to 1:2:1 instead of 1:2:2:1.

Explanation:
Incomplete dominance means that neither allele is completely dominant over the other, resulting in an intermediate phenotype in the heterozygous genotype. For example, in a cross between a red-flowered plant (RR) and a white-flowered plant (rr), the F1 generation would have pink flowers (Rr). If this cross is dihybrid, and the other pair of alleles shows complete dominance, the expected genotypic ratio would be 9:3:3:1. However, since the incomplete dominance pair only has three possible genotypes (RR, Rr, and rr), the genotypic ratio would be 1:2:1 instead of 1:2:2:1.

Conclusion:
In conclusion, when one pair of alleles shows incomplete dominance in a dihybrid cross, the genotypic ratio may differ from the expected ratio. The genotypic ratio would be 1:2:1 instead of 1:2:2:1, due to the presence of an intermediate phenotype in the heterozygous genotype.