Cells have in place a number of mechanisms to protect the integrity of the genome, including processes that repair mistakes that may occur during DNA replication. The enzyme Dna2 participates in DNA repair, but little is known about the consequences of its absence on chromosome instability. A study published in the journal Nature by researchers from several institutions, including Baylor College of Medicine, reveals that when Dna2 is absent, small DNA fragments jump from all over the genome into chromosome breaks. This novel mechanism may explain similar events commonly seen in cancer or during antibody diversification.