In fruit flies, the gene for red eyes (r is dominant and the gene for sepia eyes (r is recessive. if a red-eyed heterozygous fly (rr mates with a sepia-eyed homozygous fly (rr, what are the possible genotypes of their offspring? (hint: you many want to complete a punnett square.

The answer is Rr and rr.

R - dominant allele for red eyes
r - recessive allele for sepia eyes

If a red-eyed heterozygous fly Rr mates with a sepia-eyed homozygous fly rr, the possible genotypes of the offspring are Rr (heterozygotes) and rr (recessive homozygotes).
Parents:                Rr      x       rr
Offspring:         Rr       Rr     rr       rr

Thus, half of the offspring will have genotype RR and will have red eyes while half of the offspring will have genotype rr and will have sepia eyes.