When chromosomes are copied and divided properly, a parent cell gives rise to two identical daughter cells that function properly. But when DNA damage occurs, the genetic code contained on the DNA strands can become corrupted, leading to errors that change the behavior of cells and may ultimately lead to cancer. A particularly dangerous type of DNA damage is called a double-strand break, in which the two strands of the DNA double helix break in the same place, making it difficult for a cell to repair itself. One mechanism that cells use to repair such breaks is called homologous recombination. In this process, a cell finds a DNA sequence in the genome that resembles the sequence next to the break site and mends the break by copying that undamaged sequence.
In 2011 Memorial Sloan-Kettering researchers published several important studies that provided new insights into this and related biological processes that are fundamental to life — from the birth of a new cell to sexual reproduction and fertility to aging — but can lead to cancer or other conditions when it malfunctions.