Final answer:
Bloom's syndrome is caused by a mutation in the BLM DNA helicase gene, which is crucial for DNA replication and repair. A defect in the BLM gene can lead to increased cancer risk.
Step-by-step explanation:
Bloom's syndrome is caused by a mutation in the BLM DNA helicase gene. The BLM gene is responsible for unwinding DNA during the replication process and fixing errors that may occur during this process. A defect in this gene leads to increased levels of sister chromatid exchange and a predisposition to various types of cancer. Understanding the roles of different enzymes and proteins, like DNA helicase, is crucial in the study of genetic disorders and their mechanisms.