The Y chromosome, which is found only in males, is difficult to decode even with the latest sequencing technologies. Among evolutionary biologists, the question as to which genes lie on the male sex chromosome and where they came from is therefore hotly debated. Using an innovative analysis method, a team of population geneticists from Vetmeduni Vienna have now made a crucial breakthrough. They were able to show that genetic material in fruit flies is often transferred to the Y chromosome from the other chromosomes. Although this transfer largely occurs as a result of “accidents,” the researchers now demonstrate that some of these transfers create functional genes on the Y chromosome. The findings, published in PNAS, will supply new momentum for the research of the male chromosome in other species.