You have a linear DNA fragment of 1600 bp. To characterize it, you decide to make a restriction map. Cutting with one enzyme, you show by electrophoresis that the fragments produced are 400 and 1200 bp. Cutting the same DNA with another enzyme you recover 700 and 900 bp fragments. After treatment with both enzymes, fragments were 300, 400, and 900 bp. Which of the following order of fragments, if any, best represents the restriction map?
A) 400/ 300/ 900
B) 900/ 400/ 300
C) 400/ 900/ 300
D) 300/ 400/ 900
E) It is not possible to determine the order.

Question

Quizplus · Accepted Answer

The restriction map can be determined from the given data. When cut with the first enzyme, the DNA yields fragments of 400 and 1200 bp, indicating a single cut. The second enzyme produces 700 and 900 bp fragments, suggesting a different single cut. When both enzymes are used, the fragments are 300, 400, and 900 bp. The presence of a 400 bp fragment in both single enzyme digests and the double digest confirms its position. The 900 bp fragment from the second enzyme digest remains unchanged in the double digest, indicating it's at one end. The 300 bp fragment appears only after the double digest, suggesting it's a part of the 700 bp fragment when cut further by the first enzyme. Therefore, the correct order is 400 bp, followed by 300 bp, ending with the 900 bp fragment.

You Have a Linear DNA Fragment of 1600 Bp