Chapter 4, Problem 22P

Xerodermapigmentosum (XP) is an autosomal recessive condition characterized by moderate to severe sensitivity to ultraviolet (UV) light. Patients develop multiple skin lesions on UV-exposed skin, and skin cancers often develop as a result. XP is caused by deficient repair of DNA damage from UV exposure. a. Many genes are known to be involved in repair of UVinduced DNA damage, and several of these genes are implicated in XP. What genetic phenomenon is illustrated by XP? b. A series of $\text{10}$ skin-cell lines was grown from different XP patients. Cells from these lines were fused, and the heterokaryons were tested for genetic complementation by assaying their ability to repair DNA damage caused by a moderate amount of UV exposure. In the table below, + indicates that the fusion cell line performs normal DNA damage mutation repair, and - indicates defective DNA repair. Use this information to determine how many DNA-repair genes are mutated in the $\text{10}$ cell lines, and identify which cell lines share the same mutated genes.