Expected Phenotypic Ratios in a Dihybrid Cross without Independent Assortment?

You have two pure-breeding mutant lines (A and B) of Arabidopsis thaliana at your disposal. You want to determine if the two mutations are on the same gene or not. To answer this, I would cross the two parental lines and then self the F1 generation. The phenotypic ratios of the F2 generation would tell me whether the mutations are on different genes or not. I understand that a 9:7 ratio would by seen if they assorted independently, but if they didn't, I am unsure of what would happen.

Here is an attempt:
Ab/Ab x aB/aB -> all Ab/aB.
Ab/aB x  Ab/aB -> 1/4 Ab/Ab, 1/2 Ab/aB, and 1/4 aB/aB. This gives a 1:1 phenotypic ratio, although I assumed that this would work like a monohybrid cross and result in a 3:1 ratio, which makes me think I am doing something wrong here.

Thank you in advance for any assistance!