The figure below shows a karyotype from a normal boy. A karyotype is a photograph of a magnified view of the chromosomes from a human cell, with pairs of homologous chromosomes arranged next to each other and numbered. An extra copy of any of the chromosomes in the top row results in such severe abnormalities that the embryo always dies. In contrast, an extra copy of chromosome 21 results in less severe abnormalities so the embryo can often survive to be born as a baby with Down syndrome. What do you think is the reason for this difference?

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.)