The DNA of our chromosomes contains our genetic information. Cells must spare no effort in making sure that the integrity of the genetic information is maintained. Errors in the repair of broken chromosomes can lead to aberrant genetic information. In turn, this can lead to cancer. In this application, we propose to understand how cells select the optimal means to repair broken chromosomes. We will focus our experiments on understanding the key step in this decision process. We build this application on exciting work that have identified new proteins that participate in this process. Furthermore, the knowledge we will acquire through the proposed research will have a direct impact on our fight against some familial breast and ovarian cancers.