The basic procedure involved in synsis of recombinant DNA molecule is depicted below. The mistake in procedure is _______________.

Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites but between the same two bases of the opposite strands. This leaves single-stranded unpaired bases at cut ends. These ends with unpaired bases are called sticky ends or cohesive ends. The latter are named so because they form hydrogen bonds with their complementary cut counter parts. The sticky ends facilitate the action of the enzyme DNA ligase. Hence, the same restriction enzyme is used to create the same sticky ends which may further combine to produce a recombinant DNA molecule.