Final answer:
The statement is false; mutations in proto-oncogenes are usually dominant due to gain-of-function, leading to cancer, while tumor-suppressor gene mutations are typically recessive, requiring both copies to be mutated.
Step-by-step explanation:
The statement that mutations in proto-oncogenes are usually recessive, while those in tumor-suppressor genes are usually dominant is False. This is because proto-oncogenes behave dominantly; a mutation in just one copy of the gene can lead to a gain-of-function, which in turn can cause the gene to become an oncogene and potentially lead to cancer. This is contrasted by tumor-suppressor genes, where typically both copies of the gene need to be mutated (recessive) to lose function and contribute to cancer development. However, sometimes a single mutated allele of a tumor suppressor gene can exert a dominant negative effect, rendering the normal allele non-functional.