Xeroderma pigmentosa is due to:
Ans: b (Nucleotide excision defect) Ref: Vasudevan, 4th ed, p. 403; 5th ed, p. 421Steps in nucleotide excision repair:Repair: Excision endonuclease makes nick on both sides of thymine dimer and removes defective DNA. DNA polymerase fill the gap by synthesising DNA in 5'-3' direction. DNA Ligase seals the nick in the repaired strand .Most DNA repair occurs in G1 phase. Mismatch repair occurs in G2 phase.
Base excision defect
Nucleotide excision defect
Sos repair defect
Cross linking defect
Molecular Genetics