Maps of Fruit Fly Chromatin (IMAGE) Washington University in St. Louis Caption The fruit fly has four pairs of chromosomes: an X/Y pair (the chromosomes in the illustration are from a male fly cell but just the X is shown because the Y is very difficult to map) and three autosomes labeled 2, 3, and 4. The fourth chromosome (bottom right) is so tiny that it is often ignored. Credit Chromatin modENCODE team and Nature Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.