DNA Fingerprinting

Introduction

DNA FINGERPRINTING, or genotyping, is a common name that has been given to several DNA—based methodologies for determining the DNA signature or genetic identity of an individual that differentiates him or her from another individual of the same species. Use of DNA fingerprinting is important for research involving cultured stem cells (SCs) because of the need to guarantee the genetic identity of the SC line being studied and the fact that many studies of cultured human SCs have demonstrated a significant level of intras—pecies and interspecies cross—contamination. Historically, cross—contamination of cultured cells has been a major problem, with long—reaching repercussions, emphasizing the need to use DNA fingerprinting to prevent the use of accidentally cross—contaminated cultured human SCs (Rudin, 137).

DNA Fingerprinting

Deoxyribonucleic acid, or DNA, is the genetic information contained within the nucleus of cells. It is found in all living cells in the body and determines how the body grows and develops; it is essentially a recipe book for life. DNA controls inherited characteristics, such as the color of one's eyes and hair. DNA is made up of many millions of pieces of discrete information, and their exact combination in any person is unique except for identical twins, who share the same DNA. DNA testing, sometimes called DNA profiling or fingerprinting, does not examine a person's entire DNA; instead, it focuses on a few highly variable components of the genetic code. This means that a DNA test gives a probability that two samples with the same genetic components come from the same person, a related person, or an unrelated person.

The techniques behind DNA testing were first developed in the United Kingdom by Sir Alec Jeffreys at the University of Leicester in 1984. Professor Jeffreys was a microbiologist studying inherited genetic variations between people. While he was examining the human myoglobin gene, he noticed what he called a "minisatellite"—a small sequence of DNA that was repeated many times and was theoretically open to a number of slight variations due to mutation and replication. By using these minisatellites as landmarks, Jeffreys was able to find and analyze systematically the differences in people's DNA (Palmer, 6).

DNA Sequencing and fingerprinting

DNA sequencing is a scientific method for determining the order of the nucleotide bases in an unknown strand of DNA. The original method was devised in the early 1970s by Walter Gilbert and Allan Maxam and called Maxam-Gilbert sequencing. Their method was very labor-intensive and involved the use of hazardous chemicals. In 1975, Frederick Sanger developed a quicker, more reliable, and less hazardous method of DNA sequencing called the Sanger method or chain-termination method. This method involves the use of dideoxynucleotides (ddATP, ddTTP, ddCTP, and ddGTP), which are different from normal nucleotides in that they lack a hydroxyl group. Because they lack a hydroxyl group, they interrupt and stop the normal sequence being produced in the complementary strand from the template DNA, which causes a termination in the chain. This termination takes place at that dideoxynucleotide's spot (A, T, C, or G). This method ...