Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 1

QUANTITATIVE Restriction Mapping of DNA. The genome of a newly discovered bacteriophage is a linear DNA molecule 10,500 nucleotide pairs in length. One sample of this DNA has been incubated with restriction enzyme X and another sample with restriction enzyme Y. The lengths (in thousands of base pairs)of the restriction fragments produced by the two enzymes have been determined by gel electrophoresis to be as follows:
Enzyme X: Fragment X1 = 4.5; X2 = 3.6; X3 = 2.4
Enzyme Y: Fragment Y1 = 5.2; Y2 = 3.8; Y3 = 1.5
Next, the fragments from the enzyme X reaction are isolated and treated with enzyme Y, and the fragments from the enzyme Y reaction are treated with enzyme X. The results are as follows:
X fragments treated with Y: X - 1 4.5 (unchanged)
X 2 2.1 + 1.5
X 3 1.7 + 0.7
Y fragments treated with X:Y 1 4.5 + 0.7
Y - 2 2.1 + 1.7
Y 3 1.5 (unchanged)
Draw a restriction map of the phage DNA, indicating the positions of all enzyme X and enzyme Y restriction sites and the lengths of DNA between them.