Terminal Deoxynucleotide Transferase - Terminal deoxynucleotide transferase is a polymerase which adds nucleotides at 3' -OH end (like klenow fragment) but does not require any complementary sequence and does not copy any DNA sequence (unlike klenow fragment).

Terminal deoxynucleotide transferase (TDNT) adds nucleotide whatever comes into its active site and it does not show any preference for any nucleotide