Final answer:
A proto-oncogene is a normal gene that can transform into an oncogene through mutation, causing uncontrolled cell division and cancer.
Step-by-step explanation:
A proto-oncogene is a normal gene that can become an oncogene (cancer-causing gene) through mutation. These genes normally promote cell growth and reproduction, but when mutated, they can cause uncontrolled cell division and lead to cancer. Proto-oncogenes can be activated by various mutations, such as gene amplification, chromosomal rearrangements, or point mutations, which result in the overexpression or increased activity of the gene product.