DNA

Introduction

Genes make up 5 percent of the human genome. The other 95 percent are non-coding sequences, which used to be called junk DNA. In non-coding regions there are identical repeat sequences of DNA, which can be repeated anywhere from one to 30 times in a row. These regions are called variable number tandem repeats (VNTRs). The number of tandem repeats at specific places, called loci, on chromosomes varies between individuals. For any given VNTR loci in an individual’s DNA, there will be a certain number of repeats. The higher the number of loci that are analyzed, the smaller the probability to find two unrelated individuals with the same DNA profile.

DNA profiling determines the number of VNTR repeats at a number of distinctive loci and uses it to create an individual’s DNA profile. The main steps to create a DNA profile are: isolate the DNA from a sample such as blood, saliva, hair, semen, or tissue, cut the DNA up into shorter fragments containing known VNTR areas, sort the DNA fragments by size, and compare the DNA fragments in different samples.

The benefit of using DNA as a biometric identifier is the level of accuracy offered: the chance of two individuals sharing the same DNA profile is less than one in a 100 billion with 26 different bands studied.