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Forensic Biology
Article by: Steven Lee, Forensic Science Group, Justice Studies Department, San Jose University, San Jose, California.
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The scientific analysis of biological evidence to provide
objective information on legal matters or those that pertain
to criminal and civil law. Biological evidence such as bodily flu-
ids or tissues that may be found at crime scenes can be analyzed
through deoxyribonucleic acid (DNA) typing. Typing requires
detection and screening of the biological evidence, such as
blood, semen, or saliva, extracting the DNA from a specimen,
amplifying specific regions of the DNA using the polymerase
chain reaction (PCR), and typing the resulting PCR products to
determine a DNA profile. The DNA profile from the evidence is
then compared to known profiles from suspects, victims, or
database samples to determine the significance of the result
(Fig. 1). Samples containing mixtures require additional inter-
pretation to infer individual donor allele designations. Forensic
biologists must also assess the statistical significance of their
results, write reports, and testify in court.
Two main principles permit the use of DNA in forensics. First, no
two individuals have the same DNA, with the exception of iden-
tical twins. Second, the DNA from any source (such as blood,
hair, or skin) of a particular individual will be the same.
By comparison of the DNA profile from crime scene samples
to known samples, the results can serve to link victims and
suspects with the crime scene or can exclude a suspect from
association with that crime. Additionally, scientific analysis
of biological evidence may provide unbiased information to
substantiate case circumstances, corroborate or refute an alibi,
or identify a weapon used in a crime. Cases may include
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Key Concepts
• Forensic biology uses biological evidence, such as bodily fluids or tissues, to provide objective information
on legal matters.
• Forensic biologists rely heavily on DNA typing, because (1) with the exception of identical twins, no two individuals
have the same DNA, and (2) the DNA from any source of a particular individual will be the same.
• Biological forensics begins with visual examination, such as using UV light to detect stains, and progresses to analytical
procedures, including microscopy and chemical tests.
• DNA typing involves extracting DNA from a sample, quantification of the DNA, DNA amplification using the polymerase
chain reaction (PCR) method, DNA separation and detection, and interpretation.
• A DNA profile can be compared to known samples in order to corroborate or refute other evidence.
Fig. 1: An example of a DNA profile.
(Credit: iStock.)
