One of the easiest ways to visualize a fragment or circular piece of DNA being c

Question

One of the easiest ways to visualize a fragment or circular piece of DNA being cut by restriction enzymes and figuring out the resulting fragment sizes is to draw what is called a restriction map with the information you have.

Say, for example you know your fragment is 10,000bp long. Say when you cut with only BamHI it results in two 5000bp fragments and when you cut with only EcoR I it results in a 2000bp fragment and an 8000bp fragment. Based on this, you might draw a restriction map that looks like the following:

Using this map, answer the following questions: How many DNA fragments will be produced by digesting with both BamHI and EcoRI at the same time (known as a double digest)? What is the size of each fragment?

Explanation / Answer

Three fragments will be produced by the two enzymes with sizes: 2000 bp, 5000 bp and 3000 bp. One fragment will be of 2000 bp produced by EcoRI. The second and larger fragment produced by EcoR I of 8000 bp will be cleaved by BamHI into 5000bp and 3000bp. This is how double digest will result.

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