DNA Analysis

DNA (deoxyribonucleic acid) testing is a scientific method used to distinguish among living entities through the variations between strands of DNA. It is hard to believe that the use of DNA testing first entered the forensic world just 25 years ago. From the criminal cases shown by the media to the new popular television series CSI, the importance of DNA analysis is well-known.(Butler, 2001)

The advancement in science and technology has allowed the development of DNA testing techniques, allowing scientists to solve questions once deemed unsolvable.(Jones, 2002) Not only are we able to determine who the rightful father is in a parental dispute or the guilty party in a criminal investigation, but technology now has the ability to uncover the identity of thousands of body fragments from the September 11, 2001, terrorist attack on the World Trade Center, in New York City.

Furthermore, the use of DNA testing has played a significant role in tracing back human ancestry. By following mitochondrial DNA back through time, one is able to track the migration of specific genes through maternal lineages. DNA testing has greatly enhanced human curiosity and our understanding of the world in which we live.

Genetics and Molecular Biology

DNA is the foundation of life. Within each living cell, there is a nucleus that holds thousands of paired genes within structures called chromosomes. In human beings (who are considered normal), there are 46 chromosomes composed of strands of DNA, which include 22 pairs of non-sex-determining chromosomes (autosomes), along with one pair of sex-determining-chromosomes; an X chromosome from the mother and an X or Y from the father. The sex chromosomes determine whether the child will be male (XY) or female (XX). Except for sperm and egg cells and cells that do not have a nucleus, such as blood cells, the genetic makeup of our entire body is in every cell.

The double-helix “rope ladder” structure of DNA was discovered by James Watson and Francis Crick in 1953. They found that within each chromosome are strands of DNA, which are composed of long chains of base pairs: guanine (G), adenine (A), thiamine (T), and cytosine (C). The chemical properties allow Base A on one strand to pair with T on the other, and G to pair with C. Thus, depending upon the specific order and pairings, a gene that consists of various lengths of base pairs encodes for specific proteins. This instructional ability does not include every length of DNA, for the majority of DNA has no known function.(Jones, 2002) The locus is the molecular location of a gene along a strand of DNA, and every chromosome contains a specific order of loci, which is the same in all humans. For example, on Chromosome 7 in every human, there is a gene that, if altered, may cause cystic fibrosis.(Butler, 2001)

The Advancement in Testing Techniques

The first method of DNA testing used by forensic labs was restriction fragment length polymorphism (RFLP). Although it was first discovered in 1980 by David Botstein and coworkers, it was Sir ...