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A restriction map is a map of known restriction sites within a sequence of DNA. Restriction sites are sites on DNA where restriction enzymes, can cleave the DNA at or near the site. In molecular biology, restriction maps are used as a reference to engineer plasmids or other relatively short pieces of DNA, and sometimes for longer genomic DNA.
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There are several valid approaches to construct a restriction map of a DNA sequence. One approach is to sequence the whole molecule and to run the sequence through a computer program that will find the recognition sites that are present for every restriction enzyme known. However, restriction maps are traditionally determined by gel electrophoresis. [1] There are other ways of mapping features on DNA for longer length DNA molecules, such as mapping by transduction. [2]
Before sequencing was automated, it would have been prohibitively expensive to sequence an entire DNA strand. To find the relative positions of restriction sites on a plasmid, a technique involving single and double restriction digests is used. Based on the sizes of the resultant DNA fragments the positions of the sites can be inferred. Restriction mapping is a very useful technique when used for determining the orientation of an insert in a cloning vector, by mapping the position of an off-center restriction site in the insert. [3]