Viroids differ from viruses in having Option 1 : DNA molecules without protein coatOption 2 : RNA molecules with protein coatOption 3 : RNA molecules without protein coatOption 4 : DNA molecules with protein coat

Which of the following is commonly used as a vector for introducing a DNA fragment in human lymphocytes? Option 1 : l phage Option 2 : Retrovirus Option 3 : Ti plasmid Option 4 : pBR 322 The correct answer is Option 2