Final answer:
Gain-of-function mutations in tumor suppressor genes are typically recessive and require mutations in both gene copies but can sometimes have a dominant negative effect. Proto-oncogenes become oncogenes and promote uncontrolled cell division with just one mutated gene copy. Such mutations can be inherited if they occur in germ cells.
Step-by-step explanation:
Gain-of-function mutations in tumor suppressor genes typically result in a loss of function, where the gene loses its ability to regulate cell division properly. These mutations are often recessive and need to occur in both gene copies to affect the cell's function significantly - one mutated allele may not be enough as the other copy can still maintain the gene's function. However, in some cases, a dominant negative effect can occur where one mutated gene copy impairs the function of the remaining normal copy.
Oncogenes are mutated forms of proto-oncogenes and promote uncontrolled cell division. A gain-of-function mutation in a proto-oncogene can transform it into an oncogene, leading to cancer. These mutations are usually dominant because only one mutated copy can lead to increased cell division.
Once a mutation has occurred and if the mutated cells divide, they can be inherited by viable progeny in the next generation. This is because the mutations, if present in cells that give rise to gametes, can be passed on.