Chromosomes are the fundamental structural units of our genome. The Sfeir lab seeks to understand basic chromosome biology and how their mismanagement manifests in disease. Our research is focused on three major areas: telomere maintenance, nuclear DNA repair, and mitochondrial DNA replication and repair. A number of projects in the lab address fundamental questions related to telomere maintenance and how telomere dysfunction impacts cancer. In addition, we study an ancient yet error-prone DNA repair pathway, termed micro-homology mediated end-joining (MMEJ), and focus on polymerase theta (Polq), a key enzyme underlying mutagenic repair. Lastly, we investigate replication and repair of mitochondrial genomes and explore mitochondrial-nuclear crosstalk in response to mitochondrial DNA stress.