Carriers of Robertsonian chromosomes are often unaware they’re different. Although generally healthy, they can be infertile or suffer miscarriages. When they do have children, they’re at increased risk of having Down syndrome. Now, in a landmark study, scientists at the Stowers Institute for Medical Research have identified the precise location where human chromosomes break and recombine to form Robertsonian chromosomes. The findings, published in Nature on September 24, 2025, not only explain how these rearrangements form and remain stable—but also point to how repetitive DNA once dismissed as “junk” may play a central role in genome organization and evolution.