As part of their research published in Communications Biology, they also identified the earliest known person with Jacob's syndrome (characterized by an extra Y chromosome—XYY) in the Early Medieval Period, three people with Klinefelter syndrome (characterized by an extra X chromosome—XXY) across a range of time periods, and an infant with Down Syndrome from the Iron Age.Most cells in the human body have 23 pairs of DNA molecules called chromosomes, and the sex chromosomes are typically XX (female) or XY (male), although there are differences in sexual development. Aneuploidy occurs when a person's cells have an extra or missing chromosome....
