Chargaff wrote: "DNA is in its composition characteristic of the species from which it is derived. This can ... be demonstrated by determining the ratios in which the individual purines and pyrimidines occur
There appear to exist two main groups of DNA, namely the 'A-T type,' in which adenine and thymine
predominate, and the 'G-C type,' in which guanine and cytosine are the major constituents."
1. What does this mean? Put Chargaff's ideas above into your own words.

Mr. j, age 42, is a construction worker in las vegas. he recently noticed that a mole on his face seemed to be getting larger and darker. at first he did not worry because he was in the sun a lot and assumed the change may have been caused by sunburn. after a month, not only was the mole larger and darker, but it appeared to be “bumpy.” his doctor diagnosed a malignant melanoma skin cancer following biopsy of the nevus. mr. j reports pain in his right shin that does not go away when he puts his feet up or sleeps. discussion questions 1. relate mr. j’s skin changes to the warning signs for malignant melanoma. (see malignant melanoma.) 2. discuss the normal progression of this malignancy. what is the significance of the bone pain that mr. j is experiencing? (see malignant melanoma.) 3. discuss the treatment available for this patient and the prognosis for recovery. (see malignant melanoma.)