A colleague of yours is asked to develop a strain of mutant mice that will be extremely likely to develop cancer so that these mice can be used to study cancer treatments. Your colleague causes a mutation in a mouse that causes the mouse to express a proto-oncogene at greatly increased levels. However, your colleague is disappointed to find the mouse does not have cancer and asks your advice on what he should do next. What should you tell your colleague? a. You remind him that a mutation that increases the expression of a single proto-oncogene is generally not sufficient to cause cells to become cancerous. He should also cause some mutations in the mouse's DNA that cause increased expression of some of the mouse's tumor-suppressor genes. b. You tell him that he made a mistake by increasing expression of the proto-oncogene and that he should instead cause a mutation in a mouse that causes decreased expression of the proto-oncogene. In addition, you remind him that a mutation that decreases the expression of a single proto-oncogene is generally not sufficient to cause cells to become cancerous. He should also cause some mutations in the mouse's DNA that cause increased expression of some of the mouse's tumor-suppressor genes. c. You remind him that a mutation that increases the expression of a single proto-oncogene is generally not sufficient to cause cells to become cancerous. He should also cause some mutations in the mouse's DNA that cause decreased expression of some of the mouse's tumor-suppressor genes. d. You tell him that he made a mistake by increasing expression of the proto-oncogene and that he should instead cause a mutation in a mouse that causes decreased expression of the proto-oncogene.