Answer to Question 5 from November, 2005

Imagine that you've discovered a new gene called YFG that contributes to DNA repair efficiency. You notice that cells carrying YFG mutations frequently stop dividing and become senescent. Do you think that mutations in the YFG gene are likely to cause cancer? In no more than two sentences, please explain why you think YFG mutations might, or might not, lead to cancer (5 points).

This situation is reminiscent of Cockayne's Syndrome and of Trichothiodystrophy. In both cases, certain mutations affecting genes that contribute to DNA repair efficiency (for example, in the CSA or CSB genes) lead to cell senescence. These mutations do not lead to increased mutation frequencies, because the affected cells stop dividing. Cells that don't divide can't lead to cancer.

The last sentence above would have been sufficient. I gave full credit for any answer that pointed out that non-dividing cells can't become cancerous—except for certain long, complicated answers where it was clear that the person writing the answer didn't fully understand regulation of cell division.

Click here to return to list of questions from previous exams.