Chapter 9, Problem 7P

The following picture shows the ethidium bromide–stained bands revealed by gel electrophoresis of two different DNA samples digested with two different restriction enzymes. One of the DNAs is human genomic DNA, the other is the small genome of a bacteriophage (bacterial virus) that infects E. coli cells. One of the restriction enzymes is EcoRI (5′ G^AATTC 3′); the other is HpaII (5′ C^CGG 3′). For each of the four lanes on the gel (A–D), identify which of the two DNA samples was analyzed and which of the two restriction enzymes was used to digest that DNA. The arrow represents the direction of electrophoresis.