Forensic Science Essay Example: Blood and DNA Typing

Published: 2022-10-21
Forensic Science Essay Example: Blood and DNA Typing
Type of paper:  Research paper
Categories:  Forensic science
Pages: 7
Wordcount: 1804 words
16 min read

Blood typing (ABO)

Blood typing involves classifying blood based on the presence of an antigenic substance, or lack thereof, on erythrocytes surface. The antigenic substance is a protein that is inherited by the individual and is coded explicitly for in chromosome nine (James et al., 2005; Goubran, 2009, 5; Gunn, 2011). Although many systems have been devised based on these antigens, ABO and Rhesus systems are generally accepted and widespread in their use. Individuals possess type A, B, AB, or O with antigens A, B, both A & B and none respectively. Type A has anti-B antibodies; type B has anti-A antibodies while type AB has no corresponding antibodies and type O has both anti-A and anti-B antibodies (Uemura et al., 2008, 311). Rhesus factor system is an additional system that is used together with the ABO system to categorize blood-based solely on the presence or absence of the D antigen. Those red blood cells that have the antigen are deemed to be Rhesus positive (Rh+), but if the antigen is absent from the surface of the cells, then they are marked as Rhesus negative (Rh-) (Uemura et al., 2008, 312; Goubran, 2009, 5; Verma & Kumar, 2015, 21).

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Also, ABO antigens have also been confirmed as being present in other body fluids. Up to 75% of individuals have the antigen and are commonly referred to as "Secretors" while the rest are "non-secretors." The secretors have a similar All secretors have substance H, and the antigen present corresponds to their blood type. Thus, this method can be used to exclude or include a suspect if the markers are matching or not (Houck & Siegel, 2009).


Enzymes catalyze reactions within the body so that they are fast enough to maintain life. Every chemical reaction that occurs within one's body requires enzymes. As a result, there are quite many enzymes all over but not always similar. Some have been found to be under the control of polymorphic gene loci and thus manifest the genes direct different forms. These enzymes are therefore referred to as Isoenzymes (Houck & Siegel, 2009). Typing of isoenzymes is electrophoretically done such that different proteins, isoenzymes, are separated due to charge differences. Differences in the number of proteins obtained correspond to racial populations and different ethics (Gunn, 2011).


Although isoenzymes and serum are all proteins, they differ in that the former are enzymes. Like isoenzymes, therefore, they are separated through electrophoresis and can be grouped into different types (Sturgeon, 2001, 101). However, the most important of the serum-derived proteins for forensic serology are transferrin, immunoglobulin markers, protease inhibitors, and haptoglobin. Immunoglobulin markers such as Gm and Km were serologically typed while the others depended on either isoelectric focusing or electrophoresis. The type of serum protein in one individual can be different to that of the other and thus can help to differentiate two people. There are for instance two types of transferrin, and if two people have different types, then they can be so characterized (Houck & Siegel, 2009).

Hemoglobin Variants

Variation in hemoglobin is determined by genes which are passed down from one generation to another through inheritance. However, the different types that are in existence are more frequently observed in the population that it may be hard to find useful markers. Irrespective of this frequency, hemoglobin typing is done by use of electrophoresis and sometimes isoelectric focusing (Houck & Siegel, 2009).

HLA System

HLA system is based on antigens but is more complex than the methods as mentioned above. The antigens in HLA are associated with histocompatibility complex and as a result mismatches in people having transplants results in tissue rejection cases (James & Nordby, 2002). The antigens are present only in tissues, and white blood cells and their typing was done similarly to erythrocyte typing but more complex. The method had extensive use in paternity testing and other cases of disputed parentage until the emergence of DNA typing which is the most predominant method of choice by the majority nowadays (Gabriel et al., 2014, 65).

DNA typing

DNA typing involves analyzing a DNA sample from a crime scene to create a unique profile that can eventually lead to the identification of a suspect or exclusion of an individual (Jobling & Gill, 2004, 729; Yao et al., 2004, 5). Apart from identical twins, this DNA profile is unique to an individual. Unlike other methods of typing, DNA typing is confirmatory and can identify the person without any doubt. With the available technology, it is possible to obtain a profile from nuclear DNA, mDNA, or even touch DNA (Butler, 2005; (Juusola & Ballantyne, 2005, 3; Semikhodskii, 2007).

The emergence and evolvement of DNA technology have been steady and has revolutionized the field of not only serological forensics but also medicine (Raymond et al., 2009, 28). The new technology has had a significant impact on society and had, as a result, raised concern among some regarding financial cost, privacy, and individual interest. Through DNA typing a forensic serologist can uncover information considered private by most people (Buckleton et al., 2016; Butler, 2009).

DNA typing is tremendously advancing at a rapid speed with new inventions coming in one after another. RFLP-based typing approaches are continuously being improved and refined while PCR methods of DNA typing have found increased use in court cases and more light is being shed on the technique. These developments are likely to bring an increase in reliability and sensitivity of typing in DNA forensics (Butler, 2005; Word, 2003; Semikhodskii, 2007).Despite DNA typing in forensics being widespread as well as paternity testing, STR typing has also emerged as an essential method in forensics. STR typing has found use in monitoring engrafting of bone marrow after transplanting and in confirming the identity of specimens that are histological (Crespo et al., 2001, 652).

Why I can be considered an expert

As a forensic serologist, I am required to have knowledge in the analysis of body fluids and have a career dealing in both law enforcement and clinical aspects. The involvement of forensic serologists in solving crime involves examining and analyzing body fluids from the crime scene and the suspect (Williams, 2017). Clinically, they have to work in a forensic lab or a diagnostic lab where they test patient's blood for various diseases. I am an expert in this areas and have done such tests for several years that many consider me an expert (James & Nordby, 2002).

Furthermore, I have enough education with the relevant academic backing. This academic qualifications and hands-on experience in the field make me knowledgeable and skilled in serological forensics. I am also continuously being exposed to new laboratory procedures and use of advanced equipment. For me, therefore, training and advancement in my career is a continuous process with certifications accumulated as more knowledge is gained (Williams, 2017).

Forensic Serology

Forensic serology is an emergent field involving identifying and studying body fluids, their classification and how they relate to a crime. Such body fluids comprise of urine, blood, semen, fecal matter and perspirations (Saferstein et al., 2014). These fluids are essential in the determination of the identity of origin through specific tests and examinations. Different forensic serological tests are done for different fluid samples. For the identification of such body fluids collected or deposited at the crime scene, two types of tests are employed, ie presumptive tests and confirmatory tests. Presumptive tests are used primarily to direct initial investigation by giving a clue as to what the identity of the fluid stain might be. The test is highly sensitive, and its specificity is fair. However, presumptive tests can suffer from false positives due to other compounds that elicit the same reaction as the test substance. Confirmatory tests are usually done in forensic labs, although the increased technology has allowed for on-the-spot testing. The tests are highly specific to the test substance but may take more time than presumptive tests (Li, 2011, 269; Goodwin et al, 2011; Virkler & Lednev, 2009, 12).

Guarding against contamination and tampering

Handling or evidence from the crime scene is done by experts who are experienced in the collection of biological evidence (Lee & Harris, 2011; Wyatt, 2014). This is to ensure that all the materials at the crime scene that can help in solving the case are spotted sported and collected. From there, they are bagged as per the requirements and recorded using codes. The chain of custody is followed correctly and recorded up to when the evidence is presented in court. This way, the lab serologists can identify any contamination present and associate it to the individual it belongs to (Evans & Stagner, 2003, 563). It is therefore reasonably hard for contamination to affect the results. And if it does, then following the chain of custody can show where the contamination occurred (Mozayani & Noziglia, 2010; Gefrides & Welch, 2011, 15).

All ISO certified laboratories have a quality control management system that guards against contamination of evidence while it is being processed and analyzed in the lab. There is a prescribed mode of dressing in the laboratory that ensures the staff does not contaminate the evidence (Goodwin et al, 2011). All visitors that enter the lab are therefore scanned and issued with the necessary protective clothing (Rutty et al., 2003, 172). Strangers are never allowed in the working area unless it is essential and all the required precautions as stated in the protocols are followed. In addition to these safety precautions, only those pre-authorized individuals in the lab are allowed to come into contact with the evidence (Mozayani & Noziglia, 2010; Peterson & Hickman, 2005). Thus, contamination and tampering with the evidence are highly unlikely.


Buckleton, J.S., Bright, J.A. and Taylor, D. eds., 2016. Forensic DNA evidence interpretation. CRC press

Butler, J.M., 2005. Forensic DNA typing: biology, technology, and genetics of STR markers. Elsevier

Butler, J.M., 2009. Fundamentals of forensic DNA typing. Academic Press

Crespo, M., Pascual, M., Tolkoff-Rubin, N., Mauiyyedi, S., Collins, A.B., Fitzpatrick, D., Farrell, M.L., Williams, W.W., Delmonico, F.L., Cosimi, A.B. and Colvin, R.B., 2001. Acute Humoral Rejection In Renal Allograft Recipients: I. Incidence, Serology And Clinical Characteristics. Transplantation, 71(5), pp.652

Evans, M.M. and Stagner, P.A., 2003. Maintaining the chain of custody evidence handling in forensic cases. Aorn Journal, 78(4), pp.563

Gabriel, C., Furst, D., Fae, I., Wenda, S., Zollikofer, C., Mytilineos, J. and Fischer, G.F., 2014. HLA typing by nextgeneration sequencing-getting closer to reality. Tissue Antigens, 83(2), pp.65

Gefrides, L. and Welch, K., 2011. Forensic biology: Serology and DNA. In The forensic laboratory handbook procedures and practice (pp. 15). Humana Press

Goodwin, W., Linacre, A. and Hadi, S., 2011. An introduction to forensic genetics (Vol. 2). John Wiley & Sons

Goubran, H., 2009. Blood group serology. ISBT Science Series, 4(1), pp.5

Gunn, A., 2011. Essential forensic biology. John Wiley & Sons.

Houck, M.M. and Siegel, J.A., 2009. Fundamentals of forensic science. Academic Press

James, S.H. and Nordby, J.J., 2002. Forensic science: an introduction to scientific and investigative techniques. CRC press

James, S.H., Kish, P.E. and Sutton, T.P., 2005. Principles of bloodstain analysis: theory and practice. CRC Press

Jobling, M.A. and Gill, P., 2004. Encoded evidence: DNA in forensic analysis. Nature Reviews Genetics, 5(10), p.739...

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