That's right! In 1910, Thomas Hunt Morgan, while studying fruit flies (Drosophila melanogaster), discovered the phenomenon of sex linkage. He observed that certain traits, like white eyes in fruit flies, were inherited differently in male and female offspring.

This groundbreaking discovery led to the understanding that:

* Genes reside on chromosomes: Genes are located on chromosomes, not just floating freely in the cell.

* Sex chromosomes determine sex: The X and Y chromosomes determine an individual's sex.

* Genes on sex chromosomes have unique inheritance patterns: Genes located on the X chromosome, for example, are inherited differently in males and females due to the difference in their sex chromosomes (males have one X and one Y, females have two Xs).

Morgan's work was revolutionary and helped pave the way for our understanding of genetics and heredity.