Final answer:
A gene that encodes for a positive cell cycle regulator is known as a proto-oncogene, which, when mutated, can become an oncogene and contribute to cancer.
Step-by-step explanation:
A gene that codes for a positive cell cycle regulator is called a proto-oncogene. Proto-oncogenes are essential components in normal cell growth and division. However, when they are mutated, they can become oncogenes, which are capable of causing normal cells to turn cancerous. These alterations can lead to the unchecked and rapid progression of the cell cycle, potentially leading to cancer. In contrast, tumor suppressor genes encode proteins that act to restrain cell division, performing a function akin to brakes in a vehicle, and when these genes are mutated, they can fail to control the cell cycle, contributing to the development of cancer.