Answer
Proto-oncogenes act to prevent growth factors from over-stimulating cell division, which would cause tumors to form. They act in a dominant fashion, with only one mutant copy needed to lead to cancer. Tumor suppressor genes must be present in two mutated copies in a cell and thus are genetically recessive. Like proto-oncogenes, tumor suppressor genes, when mutated, lead cells to readily cross cell cycle checkpoints. This results in excessive cell division, which leads to tumors.
Work Step by Step
To answer this question, first look at the basic characteristics of proto-oncogenes and tumor suppressor genes. Make a list of these properties under headings such as "genetic behavior" and "interaction with growth factors." Then, see where similarities and differences are found to come up with the comparisons and contrasts which the question asks you to give.
