Final answer:
When two individuals heterozygous showing incomplete dominance (AaBb) mate, there are 9 different phenotypes possible due to each heterozygous locus resulting in three phenotypes, combining to yield 9 phenotype combinations. Therefore correct option is C
Step-by-step explanation:
If two individuals that are heterozygous for two traits displaying incomplete dominance (e.g., AaBb) mate and have offspring, to determine the number of different phenotypes possible we examine each locus separately and then combine the outcomes. Since incomplete dominance means that neither allele is completely dominant over the other, each heterozygous locus (Aa and Bb) will result in a third phenotype which is a blend of the two. For each gene, three phenotypes are possible (for the A gene: A phenotype, AB phenotype, and B phenotype; similarly for the B gene).
When you cross the possibilities for both genes, you multiply the number of phenotypes for each gene: 3 phenotypes for the A gene times 3 phenotypes for the B gene equals 9 combinations in total. Therefore, the number of different phenotypes possible from this cross is 9.