BRCA1 is a breast cancer susceptibility gene found in more than 80 per cent of families in which six or more family members have had breast cancer. A protein that interacts with this gene is very similar to a specialized enzyme, called a helicase, in the worm. Iris Cheung and her colleagues have demonstrated that the helicase is required to prevent the loss of DNA that is rich in guanine (one of the four components of DNA). Without the enzyme, DNA is lost in multiple sites in the worm genome, resulting in genetic instability and opening the door for normal cells to develop into tumour cells. Iris Cheung is researching how the prevention of genetic mutations in the worm may provide clues to how mutations arise and are prevented in the gene known to cause breast cancer. Findings may help improve researchers’ understanding of the development and properties of breast cancer, and potentially the development of new therapies.