Final answer:
Oncogenes are the category of genes that may cause cancer due to gain-of-function mutations. Mutated oncogenes produce constitutively activated proteins that promote the malignant phenotype of cancer cells. Multiple mutations in oncogenes and inactivation of tumor suppressor genes are necessary for the transformation of normal cells into cancer cells.
Step-by-step explanation:
Oncogenes are the category of genes that may cause cancer due to gain-of-function mutations. These genes are normally expressed at inappropriately high levels or have novel properties when altered. The mutated oncogenes promote the malignant phenotype of cancer cells by producing constitutively activated proteins. It usually requires multiple mutations in oncogenes and inactivation of tumor suppressor genes to transform a normal cell into a cancer cell.