IS THE Y-CHROMOSOME OF DROSOPHILA AN EVOLVED SUPERNUMERARY CHROMOSOME

The Y chromosomes of most Drosophila species are necessary for male fe rtility but they are not involved in sex determination. They have many puzzling properties that resemble the effects caused by B chromosomes . Classical genetic and molecular studies reveal substantial affinitie s between Y and B chromosomes and suggest that the Y chromosomes of Dr osophila are not degenerated homologues of the X chromosomes, but rath er that their Y chromosomes evolved as specialized supernumeraries sim ilar to classical B chromosomes.