4. A 12 kb linear DNA fragment is subject to single or double RE digest and agarose gel electrophoresis, to yield the gel profile shown below. The first lane contains the size marker (M). M Undigested EcoRI PVUII EcoRI control + PVuII 12000 bp 9000 bp 6000 bp - 5000 bp 4000 bp 2000 bp 1000 bp a) Explain how the name of the enzyme EcoRI is derived. b) How many sites are there for EcoRI and PvuII respectively on this DNA fragment? c) Use the sizes of the DNA bands on the gel to compile a restriction enzyme map of the DNA fragment. Indicate the positions of the restriction enzymes sites for EcoRI and PvuII on the map.