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.)
Rr only
RR, Rr, and rr
Rr and rr
RR and Rr