Xeroderma pigmentosum (XP) is an autosomal recessive condition characterized by
ID: 219243 • Letter: X
Question
Xeroderma pigmentosum (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 series of 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 to the left, “+” indicates that the fusion cell line performs normal DNA damage mutation repair, and "-" indicates defective repair. Use this information to determine how many DNA-repair genes are mutated in the 10 cell lines.
3 10-++ 1 2 3 4 5 6 7 8 9 10 MutantExplanation / Answer
non complementing groups are:
2,5,6 and 10 are mutually non complementing.
1,3 and 7 are mutually non complementing
8 and 4 make the third non complementation group
This means three DNA repair genes have been mutated
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