David Page’s lab studies the genetic differences between males and females and the biological and medical ramifications of these differences. At the core are the sex chromosomes: females have two X chromosomes, while males have an X and a Y. The Page Lab has overturned the long-held view that the influence of sex chromosome constitution (XX vs. XY) is restricted to the reproductive tract. Intrinsic differences between XX and XY cells exist across the body, likely contributing to the pervasive differences that exist between males and females in the incidence, severity, and progression of diseases that collectively affect all organ systems. A grand opportunity awaits: To understand male-female differences in disease by understanding male-female differences in healthy cells, tissues, and organs, at a molecular level and across the body.