ABSTRACT
Forensic DNA typing methods were developed by Sir Alec Jeffreys in the mid-1980s [1–3]. Prior to that time human identification was carried out using phenotypic protein markers of various types [4–5]. The problem with these markers was a lack of stability and variety; they denatured easily and there were only a few alleles for each protein. The promise of DNA was that it would greatly improve a sample's stability over that of proteins, and of course, the universality of DNA throughout the organism. Dr. Jeffreys’ breakthrough involved the discovery of hypervariable regions in the genome known as minisatellites [6]. Satellite DNA is highly repetitive DNA which was first identified as shoulders on the curve of DNA fragments separated by ultracentrifugation. By digesting DNA with specific enzymes, separating it, and performing Southern blotting to isolate the DNA in single stranded form, he was able to examine these variable regions with radioactive probes. Restriction enzymes cut DNA very precisely at targets which included sequences of bases such as CAGA; this process yielded millions of fragments of DNA. The fragments were then separated electrophoretically by size and transferred from the acrylamide gel to a membrane to facilitate identification of specific fragments. Radioactive 708probes, complimentary to the fragments on the membrane were used to identify a small fraction of the DNA fragments. The result, known as DNA fingerprinting resembled a bar code with each individual having a different pattern of the bands [7].
