Final answer:
Oncogenes are mutated forms of protooncogenes and can cause cancer through uncontrolled cell proliferation. The correct word identifying a mutation of protooncogenes is 'oncogenes'.
Step-by-step explanation:
The mutation of protooncogenes results in the formation of oncogenes, which can lead to cancer by causing uncontrolled cell growth. Proto-oncogenes are normal genes that when mutated, can become oncogenes, potentially overthrowing the normal regulation of cell growth and division. Hence, the correct answer to the question 'Which word identifies a mutation of protooncogenes?' is oncogenes.