Final answer:
The correct answer is A. Ras to RasD, as a single missense mutation in the Ras gene can cause a proto-oncogene to become an oncogene, leading to uncontrolled cell growth.
Step-by-step explanation:
Oncogenes and their precursor forms, proto-oncogenes, are vital in understanding the development of cancer. A single missense mutation in a proto-oncogene can be sufficient to convert it to an oncogene, which then has the potential to cause uncontrolled cell growth leading to cancer. One of the well-known examples of such a mutation is in the Ras gene, which can result in the production of a constitutively active Ras protein that signals for cell growth regardless of external regulatory signals.
The answer to the question which exemplifies how a single missense mutation can be sufficient to convert a proto-oncogene to an oncogene is Ras to RasD. This is because the Ras protein is involved in cell signaling pathways that control cell growth and differentiation, and a mutation leading to RasD can lead to uncontrolled cell proliferation characteristic of oncogenic transformation.
HER2 to Neu is related to gene duplication and overexpression rather than a single missense mutation. Gleevec-sensitive Bcr-Abl to Gleevec-resistant Bcr-Abl involves a different kind of mutation that confers drug resistance rather than initial oncogenic transformation.