Question

You have isolated and sequenced a region of DNA that appears to have caused tumor formation. For What types of mutations would you look to understand how that DNA causes the cancer and what is the characteristic of each type of mutation you might find?

Answer 1

Cancer-critical genes are grouped into two broad classes, according to whether the cancer risk arises from too much activity of the gene product, or too little. Genes of the first class, for which a gain-of-function mutation drives a cell toward cancer, are called proto-oncogenes; their mutant, overactive forms are called oncogenes. Genes of the second class, for which a loss-of-function mutation creates the danger, are called tumour suppressor genes.

Mutation of a single copy of a proto-oncogene can have a dominant, growth-promoting effect on a cell. Thus the oncogene can be detected by its effect when it is added—by DNA transfection, for example, or through infection with a viral vector—to the genome of a suitable type of tester cell. In the case of the tumour suppressor gene, on the other hand, the cancer-causing mutations are generally recessive: both copies of the normal gene must be removed or inactivated in the diploid somatic cell before an effect is seen.