Final answer:
An oncogene will contribute to cancer formation if overexpressed. These genes are mutated forms of proto-oncogenes and can cause uncontrolled cell growth. In contrast, tumor suppressor genes prevent uncontrolled cell division and their inactivation can also lead to cancer.
Step-by-step explanation:
A gene that will contribute to cancer formation if overexpressed is known as an oncogene. Oncogenes are mutated forms of proto-oncogenes, which are positive cell-cycle regulators. When these genes are overexpressed, they can lead to uncontrolled cell growth. For instance, the oncogene myc, when overexpressed, can cause cancers such as Burkett's Lymphoma.
In contrast, tumor suppressor genes act as negative regulators of the cell cycle and help prevent uncontrolled cell division. If these are mutated or inactivated, they can also contribute to cancer development. One real-world application of understanding the role of oncogenes is the development of targeted therapies, like Herceptin, which is used to treat certain types of breast cancer.