Division of Forensic Science
Forensic Biology Section
|
The FORENSIC BIOLOGY SECTION, formally Serology/DNA, provides scientific
analysis of biological evidence that has the potential to supply unbiased information
to:
|
- Substantiate case circumstances
- Corroborate or refute an alibi
- Identify a weapon used in a crime
- Determine the sequence of events
- Link or eliminate a suspect
- Establish a crime scene
The forensic serologist begins by evaluating the investigative
information and available evidence to understand the
nature of the case and the problem to be solved. Initially,
items of physical evidence are examined for blood, semen
or saliva. The isolated samples are identified and tested
for human origin as required. Further analysis is guided
by the investigating officer's request, case circumstances,
sample size and condition, available technology and/or
the conformance to case acceptance policy.
Classification of biological evidence by conventional serology
methods (ABO and polymorphic enzyme groupings) is no longer performed. DNA technology
is used for individualization of biological evidence in forensic casework.
|
|
|
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".
|
 In
search of samples: A serologist uses a flashlight to examine pieces of cloth
cut from a baseball hat. The hat was allegedly worn in an assault and stains resembling
blood were embedded in the material. The samples will be used in DNA testing.
|
|
|
 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.
|
| Tools of the trade: While the naked eye may be limited in what it
can see, a Luma Lite is not. Forensic biologists use the light to check for blood,
semen or other bodily fluids that may have been left behind during the commission
of a crime. Samples are then lifted from the evidence and prepared for DNA testing.
|
|
|
|
Ample DNA: A scientist prepares samples
for "amplification," a vital process in typing DNA. The samples will be placed
in a thermal cycler where the DNA is separated, copied and amplified. Through
a process of heating and cooling, the DNA is then increased to the point of detection
and duplicated 28 times. With the thermal cycler, 96 cases can be processed over
a three-hour period. |
|
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.
|
|
DNA Testing & Justice
DNA Technology has become a routine service provided by the GBI
Crime Lab on homicide, rape and violent crimes. Of the more than 700 DNA cases
processed by the lab, 59 percent resulted in the inclusion of a suspect and 25
percent excluded a suspect. These figures demonstrate the power of DNA not only
to associate an individual with a crime but also to exclude an individual from
a crime. With this kind of effectiveness, the criminal justice system is demanding
DNA testing more each year.
|
|
Back to Forensic Services
|
