Genetics & Biotechnology

DNA Fingerprinting

An off-branch of biotechnology came from techniques used to compare DNA from different species and population. DNA fingerprinting is based upon the DNA structure being different from species to species, and within a species from individual to individual. How do you compare DNA?

The technique, called restriction fragment length polymorphism analysis, is based upon restriction enzymes. Restriction enzymes have the ability to find specific sequences in a DNA molecule. These enzymes then cleave the DNA at those locations. Restriction enzymes are not so specific as to find just one place in the DNA molecule, but they cleave the DNA in many places. We then just compare the fragments of DNA.

An old technique for comparing molecules is based upon how they move through a gel matrix, either by gravity, or when an electric charge is running through the matrix. By controlling the size of the matrix, and the size of the charge, you can control how fast different fragments move through the gel matrix. The charge pulls DNA like a magnet pulls a piece of iron. But in this case, you are pulling the iron across a week magnet. In general, large molecules have more areas to bond to the gel matrix, so large fragments move slower from one end of the matrix to the other than smaller fragments. So, after pulling these DNA fragments through the gel matrix for a period of time, you can see the number of different fragments. (Note: you only see the number of differently sized fragments. So if there are three fragments of the same size, you still only see one fragment.)

After using restriction enzymes on two DNA from different individuals, then running them through a gel matrix, you can compare how similar and how different the DNA molecules are. Because you are not looking at every nucleic base, using two restriction enzymes helps see differences between different DNA better.

This technique has been used with great success by ecologist, and law enforcement. Ecologist can comparing different populations of salmon, for instance. Law enforcement can identify with more certainty which suspect to focus on in a crime.