Complex sentence: The insert is created by PCR using Taq DNA polymerase, a polymerase that lacks 3'to 5' proofreading activity and with a high probability adds a single, 3'-adenine overhang to each end of the PCR product.
Split into simpler sentences: The insert is created by PCR using Taq DNA polymerase. This polymerase lacks 3'to 5' proofreading activity and with a high probability adds a single, 3'-adenine overhang to each end of the PCR product.