Question

what observations led thomas hunt morgan to hypothesize that eye color in drosophila melanogaster was linked to sex?
only male flies with white eyes could produce offspring with white eyes.
only male flies had white eyes.
crosses of heterozygotes did not produce any flies with white eyes.
only white - eyed females and white - eyed males could produce offspring with white eyes.

Explanation:

Morgan observed that only male flies had white eyes. This sex - specific pattern of inheritance (white - eyed trait only in males) suggested a link to the sex chromosomes. In Drosophila, sex is determined by the X and Y chromosomes. Males have one X and one Y chromosome (\(XY\)), and females have two X chromosomes (\(XX\)). If a trait (like white eyes) is only present in males, it is likely that the gene for that trait is located on the X chromosome. Since males have only one X chromosome, if it carries the recessive allele for white eyes, they will express the trait. Females would need two copies (one from each parent) of the recessive allele to show white eyes, which was less common in the initial crosses.

Answer:

Only male flies had white eyes.