Scientists have completed the first telomere-to-telomere sequencing of human Robertsonian chromosomes, identifying precise DNA breakpoints within repeated SST1 sequences where chromosome arms fuse. This groundbreaking work elucidates the mechanisms driving the most common chromosome rearrangements linked to fertility issues and genetic disorders. By collaborating across genome assembly and variation expertise, researchers uncover new insights into chromosomal evolution and structural variant stability, setting a foundation for improved genetic counseling.