Course: SAT 170 Introductory Biotechnology

Unit 14 Learning Module

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Forensic Science and Biotechnology

Figure 1

Forensic science, often referred to as forensics, involves the application of science to the law. Forensic scientists use a variety of methods to collect, analyze, interpret and report findings regarding physical evidence as it pertains to criminal and civil investigations. Many of the methods currently used by forensic scientists are examples of biotechnology.

DNA analysis is often an important part of forensic investigations as it can be used for the identification of victims, if there body is otherwise unidentifiable. It can also be used to verify the presence of individuals at a crime scene which may be helpful in identifying the perpetrator.

Figure 1 - Shown here is an electrophoresis gel which highlights the fragments of DNA that are produced and examined during the DNA fingerprinting process. Such DNA analysis can confirm identity since individuals have a unique set of DNA. It can also be used to determine relatedness between individuals as relatives have a significant amount of DNA in common.

You may recall from unit 11 that we discussed a method for comparing the DNA of healthy and diseased individuals using a technique known as restriction fragment length polymorphism (RFLP) analysis. Recall that this technique takes advantage of the fact that different DNA samples collected from different individuals will have slightly different sequences. Such variations in the sequence can change the number and type of restriction sites that are present in a particular DNA sample (recall from unit 6 that a restriction site is a DNA sequence where a restriction enzyme will cut that DNA molecule). Thus, if two DNA samples are cut with the same restriction enzymes, they will be cut into different sized fragments. These differences can be examined using electrophoresis and blotting techniques (see unit 6 for a review of these techniques) which will show different banding patterns of the DNA samples. This is one example of DNA fingerprinting. We also discussed the use of single nucleotide polymorphisms, or SNPs, in unit 11. In the context of DNA fingerprinting, these SNPs which you may recall are single nucleotide changes that vary from person to person can be used to distinguish two DNA samples.

This diagram illustrates the unique restriction sites that are generated when individuals have different DNA sequences. This is the basis for RFLP analysis. | An SNP is also used in DNA fingerprinting since these variations differ from individual to individual.

Figure 2

Forensic science also relies on biotechnology methods for the purposes of serology and toxicology. The term serology refers to the fact that blood serum is often evaluated using serological methods; however, serology can be applied to most bodily fluids including semen, sweat and saliva. Serologists can identify things such as blood type, exposure to certain diseases through the presence of antibodies, the presence of certain toxins or poisons as well as an analysis of DNA. The identification of blood types of different samples can be particularly useful as it is technique that can be performed relatively quickly. This can allow forensic scientists to easily discern whether or not there is more than contributor in the case of a mixed blood sample, such as that which may occur if a perpetrator was injured during an attack of a victim. The presence or absence of particular antibodies can be particularly helpful if they represent antibodies that would or would not normally be found in the location where the crime took place. Different parts of the world have different pathogens and different vaccinations, so sometimes the presence of absence of certain antibodies can be used to rule out or to more highly consider one suspect or another. The evaluation of bodily fluids for toxins and poisons is often referred to as toxicology. This can be important in a forensic analysis to determine if a victim was intentionally exposed to a toxic compound or to evaluate the physical state of a victim at the time of a crime to determine, for example, whether or not they were intoxicated. DNA samples collected from bodily fluids can undergo DNA analysis as previously described.

Serological methods include many of those techniques which we previously discussed including the polymerase chain reaction (PCR) and the enzyme-linked immunosorbent assay (ELISA). A technique known as agglutination and the use of fluorescent antibodies are also often employed for serological analysis.

Figure 2 - Bodily fluids, including blood, can be used in forensic investigations to identify victims and perpetrators as well as to gain valuable insight into the physiological condition of those involved in a crime. Such bodily fluids are the focus of serological analysis.

Recall from unit 11 that the production of antibodies, which can be used for the purposes of ELISA, agglutination and fluorescent antibodies, is also an example of biotechnology. In unit 11 we describe how antiserum is derived from the blood of an animal that has been exposed to some form of antigen. An antigen is a substance which triggers an animal to produce antibodies. Examples of antigens include toxins and cell surface markers present in bacteria.  Thus, a sample of antiserum will contain antibodies that are ready to attack the antigen to which that animal has been exposed. Thus, we can intentionally expose certain animals to particular antigens in order to trigger the immune response which results in the production of antibodies. These antibodies can then be used in these diagnostic serological assays. For example, with agglutination, antibodies are used to precipitate blood cells or other cells from a serological sample which contain the antigen complimentary to that antibody. This is how blood typing assays are performed. To visualize the presence of particular compounds within a sample of bodily fluids, antibodies can be labeled with a fluorescent tag. Thus, the detection of this fluorescent tag can be used as an indicator of the presence of particular compounds. This is very similar to the fluorescence in situ hybridization (FISH) technique discussed in unit 7 for the detection of particular DNA sequences.

Figure 3 - Illustrated here is the process of agglutination which requires the use of antibodies (shown here as blue, y-shaped structures). The binding of an antibody to a particular compound is very specific; thus, if an antibody is detected (often through the use of fluorescent labels, as shown here as the bright green circles) it can confirm the presence of a specific compound.

Figure 3