<prompt> BRCA-1 gene lies on chromosome17182021  <response>: Refer Robbins page no 1054 Mutations in BRCA1 and BRCA2 are responsible for 80 to 90 of single gene familial breast cancers and about 3 of all breast cancers. Penetrance the percentage of carriers who develop breast cancer varies from 30 to 90 depending on the specific mutation present. Mutations in BRCA1 also markedly increase the risk of developing ovarian carcinoma, which occurs in as many as 20 to 40 of carriers. BRCA2 confers a smaller risk for ovarian carci- noma 10 to 20 but is associated more frequently with male breast cancer. BRCA1 and BRCA2 carriers are also at higher risk for other epithelial cancers, such as prostatic and pancreatic carcinomas. BRCA1 on chromosome 17q21 and BRCA2 on chro- mosome 13q12.3 are both large genes, and hundreds of different mutations distributed throughout their coding regions have been associated with familial breast cancers. 