In the fruit fly Drosophila, the genotype w+ for the red-eye allele is dominant to its allele w, the white-eye allele. If a female Drosophila of unknown genotype was crossed with a white-eyed male fly (XwY), 50% of the male and the female offspring were red-eyed, and 50% of the male and the female offspring were white-eyed. Which of the following is the genotype of the unknown female fly?