What is the genotype of a female Drosophila that produces both red-eyed and white-eyed offspring when crossed with a white-eyed male?

The genotype of a female Drosophila that produces both red-eyed and white-eyed offspring when crossed with a white-eyed male is indeed heterozygous. In Drosophila, the trait for eye color is often cited as a classic example of inheritance, where red eyes (dominant) and white eyes (recessive) are the two phenotypes.

If the female is homozygous for red eyes, all of her offspring would inherit the dominant red eye allele, resulting in no white-eyed offspring produced in the cross. Instead, the production of both red-eyed and white-eyed offspring indicates that the female must carry one copy of the dominant red eye allele and one copy of the recessive white eye allele (heterozygous). The male, being white-eyed, can only contribute the recessive allele.

Thus, when these alleles segregate during gamete formation, the resulting offspring can inherit either the dominant red eye allele or the recessive white eye allele from the female, leading to the observed phenotypic ratio in the offspring. This observation confirms that the female must be heterozygous.