The primary defect in Xeroderrna pigmentosa is: (A) Formation of thymidine dimmers, (B) Poly ADP ribose polymerase is defective, (C) Exonuclease is defective, (D) Formation of adenine dimmers.
Answer is A. In xeroderma pigmentos a; nucleotide excision repair of damaged DNA is defective due to formation of TT dimers