Complex sentence: Nucleic acid strands are capable of re-annealling when "normal" conditions are restored, but if restoration occurs too quickly, the nucleic acid strands may re-anneal imperfectly resulting in the improper pairing of bases.
Split into simpler sentences: Nucleic acid strands are capable of re-annealling when "normal" conditions are restored. Butif conditions are changed too quickly, the nucleic acid strands may re-anneal imperfectly resulting in the improper pairing of bases.