question_answer 25)

    The genes causing cancer are (a) structural genes         (b) expressor genes       (c) oncogenes                   (d) regulatory genes

Answer:

                  (c) Normal cells have genes called cellular oncogens or proto-oncogenes which are present in inactivated state, but under certain conditions (like mutation) these get transformed to cancer causing oncogens, whereas structural gene, expressor gene and regulatory genes are responsible for regulation of gene expression (operon model).