sequences, Dr. Jeffreys created the ability to perform human identity tests.
These DNA repeat regions became known as VNTRs, which stands for variable
number of tandem repeats. The technique used by Dr. Jeffreys to examine
the VNTRs was called restriction fragment length polymorphism (RFLP) because
it involved the use of a restriction enzyme to cut the regions of DNA surrounding
the VNTRs. This RFLP method was first used to help in an English immigration
case and shortly thereafter to solve a double homicide case. Since that time,
human identity testing using DNA typing methods has been widespread.
The past 15 years have seen tremendous growth in the use of DNA evidence
in crime scene investigations. Today, more than 150 public forensic laboratories
and several dozen private paternity testing laboratories conduct hundreds of
thousands of DNA tests annually in the United States.
In addition, most countries
in Europe and Asia have forensic DNA programs. The number of laboratories
around the world conducting DNA testing will continue to grow as the
technique gains in popularity within law enforcement.
Let’s go back to the early 1980s and review a murder case in England that was
the first to use DNA technology in criminal investigation. Since the Narborough
murders (discussed later in this chapter), the DNA technique has often been used
successfully in the United States, beginning in 1987 in the
involving a sexual assault. Although it has been used successfully in many criminal
trials, future issues will probably focus on the admissibility of DNA test results.
Genetic patterns found in blood or semen can be just as distinctive as fingerprints.
Traditional serology tests on bodily fluids often do not discriminate enough to
either exclude or include a suspect in a crime. DNA analysis provides much more
conclusive analysis. The unique genetic patterns found in each person’s DNA
make it possible, with a high degree of accuracy, to associate a suspect with (or
exclude a suspect from) a crime. Except in the case of identical twins, every person’s
DNA and resulting DNA pattern are different. The process of analyzing, or
“typing,” DNA begins with DNA source material such as blood or semen. After
the DNA is removed from the sample chemically, restriction enzymes known as
endonucleases are added that cut the DNA into particles or fragments. The particles
are then mixed with a sieving gel and sorted out according to size by a process
called electrophoresis. In this process, the DNA moves along the gel-coated plate,