FIGURE 6-12 Ligation of restriction fragments with complementary sticky ends. In this example, vector DNA cut with EcoRI is mixed with a sample containing restriction fragments produced by cleaving genomic DNA with several different restriction enzymes. The short base sequences composing the sticky ends of each fragment type are shown. The sticky end on the cut vector DNA (a′) base-pairs only with the complementary sticky ends on the EcoRI fragment (a) in the genomic sample. The adjacent 3′ hydroxyl and 5′ phosphate groups (red) on the base-paired fragments are then covalently joined (ligated) by T4 DNA ligase.