The EcoRI digest of λ DNA yields the following 6 discrete fragments (in base pairs): 21226*, 7421, 5804, 5643, 4878, 3530*. The cohesive ends (12b cos site of bacteriophage lambda) of fragments 21226 bp and 3530 bp may anneal and form an additional band. These fragments may be separated again by heating to 65 °C for 5 min and then cooling on ice for 3 min.