A piece of DNA that is 5,000 bp long is digested with restriction enzymes A and B, singly and together. The DNA fragments produced are separated by DNA electrophoresis and their sizes are calculated, with the following results: Digestion with A B A+ B 2,100 bp 2,500 bp 1,900 bp 1,400 bp 1,300 bp 1,000 bp 1,000 bp 500 bp 1,200 bp 800 bp 600 bp 500 bp 200 bp Each A fragment is extracted from the gel and digested with enzyme B, and each B fragment extracted from the gel and digested with enzyme A. The sizes of the resulting DNA fragments are determined by gel electrophoresis, with the following results: Fragments Produced by Digestion Fragment Produced by Digestion with A A B Fragment 2,100 bp with B Fragment 1,900, 200 bp 2,500 bp 1,900, 600 bp 1,400 bp 800, 600 bp 1,300 bp → 800, 500 bp 1,000 bp 1,000 bp 1,200 bp -> 1,000, 200 bp 500 bp 500 bp Construct a restriction map of the 5,000-bp DNA fragment. ​