2. The radish has nine groups of traits. Within each group, dihybrid crosses do not yield a 9:3:3:1 phenotypic ratio. Instead, such crosses yield an overabundance of phenotypes like those of the parents. What does this information reveal about the chromosomes of this plant?

At least some of the genes are located on the same chromosome.

Explanation:

The recombination frequency determines whether the genes are located close to each other and what shall be the frequency of re-occurrence of any trait in the offspring in future. When the genes are on separate chromosomes or lie at great distances than they assort independently. For example - If the recombinant frequency is 50%, then the genes lie on different chromosome and hence they assort independently thereby reducing the chance of occurrence of trait of parent gene.  

Here in this case there exists overabundance of phenotypes like those of the parents,  hence some of the genes must be located on the same chromosome.

this transfer is call conjunction