Confused on Biology HW with Complementation Analysis

[chohlman]

Three autosomal recessive mutations in Drosophila, all with tan eye color (r1, r2, and r3), are
independently isolated and subjected to complementation analysis.
a) Based on the results shown below, which, if any, are alleles of one another?
Cross 1: r1/ r1 X r2/ r2 → F1: all wild-type eyes
Cross 2: r1/ r1 X r3/ r3 → F1: all tan eyes
b) What would be the predicted outcome of a cross between r2/ r2 X r3/ r3?

Our teacher hasn't gone over complementation analysis and I tried reading up on it in our text book and still can't seem to understand what this question is asking for....can anybody please help explain it to me!?

[JackBean]

You have three mutations, which cause all the same phenotype. That could suggest, they are all caused by mutation in only one gene, right?
Thus you take homozygotes and make a cross. If the mutations were both on the same locus, the offspring would bear the recessive phenotype. But if it is on different loci, the offspring will have on both loci one mutated version and one normal, thus the phenotype will be normal

Clear now?