When Thomas Hunt Morgan crossed red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

• A. The gene involved is located on the Y chromosome.
• B. The gene involved is located on the X chromosome.
• C. The gene involved is located on an autosome, but only in males.
• D. Other male-specific factors influence eye color in flies.

Answer: (B)

Verified step by step guidance

1. Understand that Thomas Hunt Morgan's experiment involved Drosophila melanogaster (fruit flies), where eye color is a sex-linked trait.
2. Recognize that sex-linked traits are often associated with genes located on the sex chromosomes, X and Y. In Drosophila, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).
3. Consider that the presence of white-eyed males in the F2 generation suggests that the gene for eye color is located on the X chromosome. This is because males inherit their single X chromosome from their mother and their Y chromosome from their father.
4. Realize that if the gene were located on the Y chromosome, females would not be able to express the trait, as they do not inherit a Y chromosome. The presence of white-eyed males indicates that the gene is not on the Y chromosome.
5. Conclude that the gene for eye color must be located on the X chromosome, as this explains why only males (who have a single X chromosome) can express the recessive white-eye trait when they inherit the X chromosome carrying the white-eye allele from their mother.