RFLP

The following information is taken from Dr. Donald Riley, Ph.D (Citation 4).

"RFLP [restriction fragment length polymorphism] has been almost entirely replaced by PCR-based testing.  The following description of RFLP is included here primarily for historic reasons (more current formats see below).

 RFLP DNA testing has four  basic steps:

1.  The DNA from crime-scene evidence or from a reference sample is cut with something called a restriction enzyme.  The restriction enzyme recognizes a particular short sequence such as AATT  that occurs many times in a given cell's DNA.  One enzyme commonly used is called Hae III (pronounced: Hay Three) but the choice of enzyme varies.   For RFLP to work, the analyst needs thousands of cells.  If thousands of cells are present from a single individual, they will all be cut in same place along their DNA by the enzyme because each cells DNA is identical to every other cell of that person.

2.  The cut DNA pieces are now sorted  according to size by a device called a gel.  The DNA is placed at one end of a slab of gelatin and it is drawn through the gel by an electric current.  The gel acts like a sieve allowing small DNA fragments to move more rapidly than larger ones.  

3.  After the gel has separated the DNA pieces according to size, a blot or replica of the gel is made to trap the DNA in the positions that they end up in, with small DNA fragments near one end of the blot and large ones near the other end.  The blot is now treated with a piece of DNA called a probe.  The probe is simply a piece of DNA that binds to the DNA on the blot in the position were a similar sequence (the target sequence) is located. 

4.  The size or sizes of the target DNA fragments recognized by the probe are measured.  Using the same probe and enzyme,  the test lab will perform these same steps for many people.  These sizes and how they distribute among large groups of people form a database.  From the database a rough idea of how common a given DNA size measured by a given probe is found.  The commonness of a given size of DNA fragment is called a population frequency."

RFLP explained. (Image 10)

The video above shows the process of RFLP. (Multimedia 7)