Forensic Biology: A Complete Review

What is Forensic Biology?

Forensic biology is the study of biological data to provide unbiased information on legal issues, particularly those that concern criminal and civil law.

Body fluids are subjected to serological and DNA tests by the field of forensic biology to identify and personalize the subjects. Blood, semen, and saliva gathered at crime scenes or from tangible evidence items are just a few examples of the materials that are frequently investigated. When violent crimes like killings, rapes, assaults, and hit-and-run fatalities are committed, bodily fluids of this nature are routinely produced. The end goal is to determine the kind of material that is there and then, through DNA analysis, match that material to a particular person.

Through timely scientific analysis of biological evidence, forensic biology’s services are meant to help the criminal justice system. When used properly, this testing has the potential to offer objective information: With biological evidence, one can connect or rule out a suspect. Detailing the specifics of the case Verify or disprove an alibi what weapon was used? To understand the circumstances surrounding the case and the forensic question(s) to be addressed, the forensic biologist first assesses the investigative data and accessible evidence. Physical evidence is initially checked for the presence of blood, semen, or saliva. The investigating officer’s request, case circumstances, sample size and condition, available technology, and/or compliance with case policy serve as guidelines for further research.


The traditional serology approaches (ABO and polymorphic enzyme groupings) for classifying biological evidence are no longer used. In forensic casework, DNA technology is utilized to personalize biological evidence. Biological evidence can be linked to a specific person, but the age of the sample cannot be established. The creation of a DNA database for convicted felons and those on felony probation in Georgia, as permitted by O.C.G.A. 35, is another service provided by forensic biology. The DNA profiles from casework samples can be compared to those criminals in the Georgia file using this database. Additionally, profiles are sporadically added to a national database. This database makes use of the CODIS FBI program (Combined DNA Index System).

Regular searches are conducted on both the national and Georgian databases. Cases that are filed without a suspect will be tested, and the necessary information will be placed into the CODIS system. Although DNA testing is done in these circumstances, it should be highlighted that cases with named suspects are given precedence.

Use of Serological and DNA analysis in Forensic Biology

Serological and DNA type analysis can be used to examine biological evidence, such as body fluids or tissues, that may be discovered at crime scenes. To type, biological evidence such as blood, semen, or saliva must be found and screened. DNA must then be extracted from the sample, amplified using the polymerase chain reaction (PCR), and then typed to produce a DNA profile. The relevance of the outcome is then determined by comparing the DNA profile from the evidence to known profiles from suspects, victims, or database samples. To deduce specific donor allele designations from samples that contain mixes, extra interpretation is necessary. Additionally, forensic biologists must evaluate the statistical significance of their findings, produce reports, and give depositions.

The creation of a national DNA database for the United States, known as CODIS or the Combined DNA Index System, has made it easier to link cases by comparing DNA profiles from unidentified biological crime scene evidence to DNA databases of known convicted criminals and “cold hits” or DNA left at other crime scenes. Many other nations have DNA repositories with some of the same genetic markers, enabling searches across national databases.

The results can link victims and suspects to the crime scene or rule out a suspect from being connected to that incident by comparing the DNA profile from crime scene samples to known samples.

Furthermore, unbiased information from the scientific study of biological evidence may be utilized to support case details, support or disprove an alibi, and/or pinpoint the crime’s weapon of choice. Non-human samples from plants, fungi, insects, and animals may be present in some cases. These samples can be used to connect victims and suspects or to the crime scene.

Also Read: Forensic Science In Criminal Investigation

Testing Times

Serological testing takes a long time to complete and depends on the quantity and type of supporting documents. The anticipated examination time for one item is given below: Several hours to overnight for human blood Several hours to overnight for semen Several hours to overnight: spermatozoa hours of saliva When initial exams are negative and additional testing is necessary, the longer time is typically required. These periods will also considerably increase while looking at many items. DNA analysis follows a set procedure that cannot be “rushed.” The procedures’ success depends on the paperwork and cares they demand. Typically, testing takes two to three weeks.

Sample and Evidence Handling

Any kind of biological sample is acceptable as biological evidence.

These samples could be either non-human or human. Blood, saliva, semen, and skin cells from clothing like caps or sweat stains, vaginal cells, and/or anal cells from swabs, cigarette butts, fingernail scrapings, hair, and bone are some examples of biological evidence that are frequently examined in crime labs.

To determine the nature of the case and the issue that has to be resolved, the forensic biologist first assesses the investigative data and available evidence mentioned in the crime scene investigator or officer’s report. Physical evidence is initially examined using presumptive tests for the presence of blood, semen, saliva, or other bodily fluids, as is the case.

Second, the samples’ human origin is determined using confirmatory assays. Third, DNA testing is used to personalize the bodily fluid. Before selecting the optimal technique for stain removal, forensic biologists assess an item or stain for its potential for genetic typing. The analyst must choose the number of tests to run after screening the stains to maximize information while reducing consumption. Additionally, the proper safeguards must be taken to reduce contamination during sample collecting, packaging, storing, and handling during analysis.

The investigating officer’s request, the facts of the case, the scope and condition of the sample, the preliminary findings, the state of the technology, and/or the adherence to the case acceptance policy all serve as guidelines for further analysis. The analyst must also properly preserve and store biological data for potential future re-analysis. Any leftover stains, DNA extracts, and amplified products from the case will be considered biological evidence. The “art” of forensic biology has been dubbed forensic detection and screening since it can make or break a case to determine which pieces of evidence will show to be the most instructive or probative.

Other sample considerations

Due to the nature of the samples, forensic biologists also have to contend with three other difficulties when conducting their tests. First, mixes of two or more people may be present in the samples. Sorting the victim’s alleles from those of the suspect(s) or point of interest is necessary (person of interest). Samples of sexual assault may include a combination of the male offender and the female victim. There may be more than one suspect in complicated circumstances. In addition to being destroyed by a range of environmental stressors, samples may also contain substances that impede the performance of downstream analytical techniques like PCR.

As a biological sample, the sample’s biology as well as the molecular biology and genetics of the loci being typed must all be thoroughly understood. Validation guidelines for forensic DNA typing laboratories address several of these difficulties.

 Examples of Biological evidence

  • Blood
  • Saliva (envelopes, cigarette butts, bite marks)
  • Semen
  • Skin (fingerprints, touch samples)
  • Hair
  • Bone
  • Mucus
  • Ear Wax
  • Vaginal and rectal cells
  • Urine
  • Vomitus
  • Fecal matter
  • Tissues
  • Teeth
  • Plant material
  • Animal tissue or hair
  • Microbes- bacteria, fungi, viruses

Forensic DNA

Alec Jeffreys pioneered the use of DNA forensics in two rape-homicide cases in Leicester, England, in 1985. Living cells include DNA in their nuclei, mitochondria, and chloroplasts (in plants). The genetic code that determines a person’s unique features is stored in chromosomes inside the nucleus. In other words, DNA serves as the “blueprint” of each person. DNA can be used in forensics under two major conditions. First, unless they are identical twins, no two people have the same DNA.

Second, the DNA in blood, hair, skin, or any other biological material from a single human will be the same regardless of where it comes from.


DNA must be extracted when the samples have been found and screened. There are various extraction techniques. The first one is organic extraction. Cells are first lysed in a detergent-based buffer, then purified using an organic phase separation (in phenol-chloroform-isoamyl alcohol: Tris EDTA), concentrated using column centrifugation or ethanol precipitation, and finally extracted using Chelex resin. This approach makes use of a chelating resin and a quick, straightforward extraction of small amounts of material. The technique yields an extract that is a little rough, but it is typically sufficient for PCR amplification of the forensic genetic loci.

Techniques for solid phase extraction.

These techniques, like the FTA paper approach, use a membrane that serves as a DNA capture device. Samples are spotted onto the membranes, and then the contaminants are washed away.

Methods of extraction based on silica.

In these procedures, chaotropic salts like guanidine hydrochloride are used to first adsorb nucleic acids on the silica surface. These salts dehydrate molecules in solution by removing the water. Proteins and polysaccharides do not adsorb and are excreted. Next, pure nucleic acids are released after being washed with low salt. Numerous crime labs are adopting this technique, which has been automated using robotic stations.


The next stage is to evaluate the sample’s size and quality. In crime laboratories, several techniques are applied. These include

1) yield gel electrophoresis, which involves running agarose gel electrophoresis in the presence of quantification standards (DNA samples with known concentrations);

2) slot blot hybridization, which involves running known DNA standards immobilized on a membrane; followed by hybridization to a DNA probe specific to humans or higher primates;

3) homogeneous plate assays using a DNA fluorescent dye and plate reader scanning; and, more recently,

4) real-time detection using quantitative The initial DNA concentrations can be determined using TaqMan assays or real-time QPCR with a 5′-nuclease fluorogenic test.

Real-time QPCR is superior to conventional procedures in several ways, including the fact that it is highly precise and sensitive over a wide dynamic range and that it takes place in a closed-tube system, minimizing the risk of carryover contamination. A forensic biologist can track and measure the buildup of PCR products during log phase amplification using this method.

STR amplification by the use of polymerase chain reaction

Fast in vitro DNA synthesis using the Polymerase Chain Reaction (PCR) can produce up to a billion copies of a given target sequence. A DNA polymerase can target particular DNA markers for duplication. For PCR, the following five chemical elements are necessary: Template (the genomic DNA from the sample that has been extracted), Primers, dNTPs, Mg++, and a thermally stable DNA polymerase, most frequently Taq polymerase.

The primers are intended to hybridize to the particular markers (such as STR loci) along the length of the template while the temperature is cycling.

The thermal cycle involves the separation of the DNA strands, the binding of primers to the template, and the use of a particular, heat-stable DNA polymerase to replicate and amplify the genetic markers with the remaining elements. The DNA is then expanded through a procedure of 28–32 heating and cooling cycles so that it may be examined.

As many as 96 samples can be amplified in under three hours using the thermal cyclers’ numerous sample wells, which allows for the simultaneous amplification of several samples.

When multiple distinct loci are amplified simultaneously in a single tube, the process is known as multiplex PCR. This reduces sample consumption and enables typing from a single aliquot of the isolated genomic DNA. Recently, it was reported that by utilizing DNA from a very tiny amount of a degraded sample, it was possible to evaluate as many as 15 autosomal short tandem repeats (STRs) simultaneously.

Separation and Detection

Following PCR, the amplified products must be separated from one another and detected.

There are a lot of various ways to type. There are two of these:

1) Capillary electrophoresis (CE) with laser-induced fluorescence and

2) Polyacrylamide gel electrophoresis (PAGE) with silver staining or if the primers are fluorescently labeled, detection by fluorescent gel scanners. Since it is highly automated (no gel needs to be loaded or poured), samples can be easily reinjected (robotically), and since the DNA traverses the entire length of the capillary, the resolution of the higher molecular weight loci is typically better than in PAGE methods, this method has become the most widely used method of detection. Crime scene samples may be typed using any of the procedures as long as they have been validated.

Forensic Genetic Markers

 The majority of forensic biology laboratories currently type autosomal short tandem repeats (STRs), mitochondrial DNA, and Y chromosome STRs as the genetic markers. Compared to their predecessors, short tandem repeats, or STRs, have significant benefits.

They are composed of tandemly repeated sections of 2–7 base pair repetitions. In the human genome, STRs are both numerous and well-studied. They can be typed from small amounts of highly degraded beginning and modified to their small size and small size range of alleles. The number of repetitions and/or the repetition’s content may differ between people. Changes to a repeat unit’s base or deletions within repeat units cause variations in the content of the repetitions.

Tetranucleotide or pentanucleotide repeats (STRs) are utilized in forensics. The national DNA database is now being updated with 13 CODIS core loci. The thirteen main loci are THO1 TPOX, CSF1PO, WA, D3S1358, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820, and D13S317.

Applications of Forensic Biology

Forensic biology’s role in disaster response and home security. There are many ways that forensic biology can be used in homeland security.

First, one of the main applications is to help link suspects to the crime or keep them from being associated with it, much like with any criminal casework.

The distinction is that in the context of homeland security, the crime could involve weapons of mass destruction (WOMs), such as pathogenic germs (like anthrax) or chemical agents.

First, forensic biologists may be requested to help type DNA from the crime scene and match the resulting DNA to databases or known suspects.

The forensic biologist may now be able to type the microbial DNA and link the strain of the microbe to a strain produced at a given site or to the original progenitor strain since the weapon of mass destruction may be biological (such as anthrax).

The purpose of the second application is to aid in the identification of terrorist attack victims. When the level of destruction is so great, as it was in the World Trade Center attacks, traditional methods of identification become impractical, and forensic DNA typing becomes crucial.

The purpose of the third application is to aid with WOM detection. Numerous organizations are working on initiatives that will allow for the quick, accurate detection of extremely small amounts of WOMs, particularly those that are the most deadly and have the most potential to spark epidemic-scale disease outbreaks. To test vast volumes of air or water and offer real-time detection of these WOMs, these biological detectors are being developed.

To help identify the perpetrators of a bioterrorist assault as well as the victims’ identities, forensic biologists must be ready to identify the attack’s agent.

Future applications of Forensic Biology

There are many applications of forensic biology that are currently under investigation.

Forensic Biometrics

Forensic biometrics refers to the capacity to identify a person’s physical traits by typing genetic markers. The community of origin can be inferred from DNA evidence utilizing Y chromosome SNPs, according to a recent study. The capacity to identify a perpetrator’s possible genetic heritage has clear advantages for law enforcement since it allows for the analysis of samples taken from crime scenes, which may yield information that is helpful for investigations. Using genetic markers to give phenotypic data has moral and legal ramifications. Furthermore, despite the blurring of racial lines, major limitations are still visible. The rights of individuals and the interests of the states must be carefully weighed, as is the case with databases and any DNA typing. Using genetic markers, forensic biometrics can also be used to establish a suspect’s age.

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