Source: Bureau   of Investigation, Division of Forensic Science*

Forensic DNA

DNA - Deoxyribonucleic Acid DNA is an organic substance found primarily in the nucleus of living cells. It comprises the chromosomes within the nucleus and provides the genetic code that determines a person's individual characteristics. In other words, DNA is the "body's blueprint".
DNA Molecule: The unique combinations possible in the chromosomes of nuclei of cells are what make individuals different from one another. Those combinations can be analyzed through DNA typing to detect the naturally occurring variability among individuals. In simplified form, DNA typing involves extracting the DNA from a specimen such as blood, semen or saliva, then amplifying specific regions of the DNA. Eventually those amplified regions are typed to determine a DNA profile. All of these sources provide the same DNA from any particular individual, so scientists are able to compare sperm DNA collected in a sexual assault case to blood DNA from potential suspects. DNA typing in criminal investigations was first introduced in England in 1985. The Georgia Bureau of Investigation began developing its DNA program in 1989 and began accepting cases from local law enforcement in January of 1991. By comparing the DNA profile of an individual�s blood with that of body fluids recovered from a sexual assault kit or crime scene, GBI Crime Lab scientists can determine if the biological specimens are from the same person. If the patterns do not match, scientists can be assured that the suspect did not leave their biological fluid.
The FORENSIC BIOLOGY SECTION continued to maintain its cutting-edge position in DNA technological advancements when the GBI lab became the first crime laboratory in the country to implement the latest method of DNA analysis, Capillary Electrophoresis (CE). This method offers tremendous potential for improvement in both turn-around time and results. The older DNA methods would take six to seven weeks to process an average case. With this latest technology, GBI scientists are looking forward to processing up to 48 samples in 24 hours with an average case turnaround time of two weeks. Additionally, Capillary Electrophoresis allows GBI scientists to look at 13 different loci and it gives the scientists the ability to determine the sex of the sample all at the same time.
Typing DNA: A forensic biologist prepares a capillary electrophoresis instrument for use. The state-of-the-art �CE� assigns DNA to samples and then charts the findings on to a computer. Scientists review the results to determine whether the profile matches that of the suspect or victim.

 

Over the years, the court challenges to the use of DNA technology have moved from the contention that the technology itself is somehow scientifically improper to attacks on the way the statistics are analyzed. The GBI Crime Lab has and will continue to interpret the statistics in a conservative and responsible manner. Another service of the FORENSIC BIOLOGY SECTION is the development of a Georgia DNA database of convicted sex offenders as authorized by Georgia law. This database allows for the comparison of DNA profiles from casework samples (when no donor has been identified) to those of previous offenders in both the Georgia file and in the national file. About 70 percent of the staff�s time involves analyzing semen for rape cases. This database is part of a nation-wide system called CODIS, Combined DNA Index System.

 

Internet Sources

 

---