Final answer:
The BRCA1 and BRCA2 proteins commonly perform DNA repair and participate in homologous recombination repair of double-stranded DNA breaks. When these proteins are mutated, efficient DNA repair is compromised, increasing the risk of breast cancer.
Step-by-step explanation:
The BRCA1 and BRCA2 proteins commonly perform DNA repair. When these proteins are functioning normally, they participate in homologous recombination repair of double-stranded DNA breaks. They bind to Rad51 and help in the repair process. However, when these proteins are mutated, they function poorly and DNA in the affected cells is not efficiently repaired, increasing the likelihood of developing breast cancer.