DNA Genetic Fingerprinting

In these times of identity theft, terrorism, and the TV criminology craze, learn just how genetic fingerprinting occurs.

Obtaining a genetic finger print begins with the sample of biological tissue. At Guys Hospital in London, this research worker is using an automatic DNA extractor to produce a high purity DNA fraction from a blood sample. A restriction enzyme is added to the DNA. This enzyme moves along the DNA’s strand, cutting it at the so called restriction sights. The restriction sights available to enzymes are located throughout the chromosomes, except in section consisting of copies of the core sequence. This process produces many pieces of DNA, which consist of repeats of the core sequence. The mixture of this DNA fragments is then place on to agarose gel. A small voltage is applied is across the gel, and the fragments move through the gel at the rate proportional to their size. Because gels are difficult to handle, the DNA bond pack on the gel is transferred to a nylon membrane by a technique known as Southern Blotting. First, the nylon membrane is place in the agarose gel. Then, absorbent paper is layered on top of the membrane. It acts as a wick, drawing up the DNA bonds on to the membrane where they stick. Finally, the researcher adds a radio active DNA probe which will bind specifically to the core sequence. Excess DNA probe is wash off leaving only the radio active probe that just bound to the DNA pattern on the membrane. This can be shown on X-ray film, producing the genetic finger print.