Forensic BiologySolving mysteries is a challenge many people enjoy. If they take a scientific approach, they are likely to use forensic sciences to examine evidence and to solve crimes. Students are commonly exposed to crime situations in the media, both fictional and real, and are likely aware that forensic sciences are used to solve crimes, as many current television programs and popular authors use the science of forensics to develop their dramas.

A forensics team is a group of scientists who work together performing different jobs to solvecrimes or to identify people. A forensics team may observe the crime scene and gather evidence such as hair and fibre samples, fingerprints, and tissue samples. An investigative team includes forensic scientists with varying areas of expertise, including toxicology, forensic biology, forensic entomology, chemistry, forensic psychology, forensic odontology, forensic anthropology, bloodstain pattern analysis, and weapons specialists.The job of forensic investigators is to use science and technology to perform tests on the evidence collected. The results from these tests can then be used to support a theory of guilt or innocence. Forensic scientists use the same instruments and techniques used by scientists doing other types of research, including microscopes, computers, gas chromatographs, and lasers. As science has advanced, so has the ability to gather evidence and to solve crimes. At crime scenes, portable lasers provide special lighting. Imaging technology lets a police officer instantly send a photograph or fingerprint image to a central data bank for identification. Computers can enhance pictures taken by a security camera at a crime scene. New chemicals allow the visualization of otherwise unseen fingerprints. Lasers can vaporize tiny portions of a paint specimen to determine the exact paint used on a car in a hit-and-run case. A single cell can provide deoxyribonucleic acid (DNA) that molecular biology techniques can match with a suspect. Forensic biology is the application of biological analysis methods, particularly serological methods, to legal investigations. Serology involves the investigation of bodily fluids, particularly the likes of blood, semen, saliva, all of which are commonly found at certain crime scenes.

There are numerous types of bodily fluid that may be found at a crime scene or on a victim, all of which have the potential to be analysed and used in the identification and incrimination of the perpetrator. The examination of such substances can not only provide clues as to the identity of the offender, but also help investigators develop a detailed picture of the sequence of events which occurred. The presence of certain bodily fluids can be excellent indicators of what has occurred. For example, the presence of semen may suggest a recent sexual encounter, whether consensual or otherwise. Perhaps more obviously, blood at a crime scene is often indicative of some form of physical struggle, assault, or even murder. The analysis of bodily fluids may also determine the presence of quantities of certain substances in the body, such as alcohol or toxins.

Bodily fluids can be divided into two categories: excreted fluids and secreted fluids. Excreted fluids that may be found at a crime scene include faeces, vomit, bile, and sebum (skin oil). Secreted fluids include blood, plasma, semen, saliva, female ejaculate, and urine.

When a potential bodily fluid is first discovered at a crime scene, actions may be required to visualise the stain. Some biological samples are difficult to see with the naked eye, and require particular light or chemical additions to reveal their presence. Presumptive tests may be conducted to give some indication as to the identity of the substance, though these tests are by no means conclusive, and further analysis will be essential. The sample must be then collected and stored appropriately so as to preserve its integrity as best as possible. Wet samples will often be swabbed, with the swab then being placed in a vial or other airtight container. Individual samples should obviously all be stored separately to prevent contamination. All biological samples are generally dried or frozen during transport and storage. If the samples are to be dried, they should be left to dry by air without the addition of heat, as heat can be damaging to such specimens. These extensive measures are taken to not only protect the samples for analysis, but also protect the staff handling the samples from biohazards, such as infection from a biological sample. The sample will then be transported to a laboratory so that the analysis can be conducted.

The primary goal of this analysis will be to establish exactly what the sample is. Though the answer may seem obvious from the appearance of the sample, conclusive tests should always be conducted. Specific tests will be discussed in more detail later on. The substance should also be subjected to species-specific tests, as the biological sample may belong to another animal rather than a human. After the completion of such confirmatory tests, DNA analysis may be conducted to attempt to identify the secretor of the sample.

A biological sample may not always contain sufficient DNA to obtain a DNA profile. Individuals may be known as secretors or non-secretors. Secretors present aspects of their bloods protein in other bodily fluids, whereas non-secretors will not have sufficient levels of protein in their bodily fluid to establish a match between two samples. Fortunately, the percentage of the population who are non-secretors is comparatively small.

BloodOne of the most common types of bodily fluid found at crime scenes, particularly the scenes of violent crimes, is blood.Blood is a tissue that is circulated within the body to assist other parts of the body. This connective tissue has specialized cells that allow it to carry out its complex functions. For a healthy person, approximately 8% of their total weight is blood. For a 70kg (154lb.) individual, this equates to 5.6L (12 US pints).Biological considerationsBlood contains three components or blood cells that are suspended withinplasma. The three components are erythrocytes, leukocytes, and platelets. Erythrocytes, also known as red blood cells, are transporters. The role of erythrocytes is to transport oxygen. To do this, they contain great quantities of hemoglobin, which carry oxygen molecules and give blood its distinct red colour. Blood that has passed through the heart and been oxygenated (oxygenated blood travels through the arteries) tends to have a brighter shade of red as opposed to blood that is returning to the heart (in the veins). There are about 30 trillion erythrocytes circulating in the human blood at any given time. Leukocytes, also known as white blood cells, are the body's defenders. The role of leukocytes is to defend against harmful bacteria, viruses and microorganisms. There are five different types of leukocytes. They all have different sizes, shapes, structures, and functions. Leukocytes fight infection and disease. There are about 430 billion leukocytes circulating in the human blood at any given time (~1 per 700 erythrocytes). Pus is made up of leukocytes left in an affected area during and after fighting harmful substances or organisms that infect the body. Plateletsare formed in the bone marrow. These particular blood cells contain cytoplasm and are enclosed by a membrane, but do not have a nucleus. They play a major role in hemostasis (control of bleeding) by plugging up a breach in a vessel. They are important for forming blood clots. If a person has an abnormally low platelet count, a condition known as thrombocytopenia, blood clots more slowly.Plasma is the yellowish fluid that carries the erythrocytes, leukocytes, and platelets. It is composed of water (92%), proteins (7%), and other materials such as salts, waste, and hormones, among others. Many of these proteins are clotting factors, which are important along with platelets for forming blood clots; clotting factor deficiencies can cause prolonged and excessive bleeding, a condition called hemophilia. Plasma makes up about 55% of blood. The remaining 45% is the blood cells. Because plasma is less dense than the blood cells, it can be easily separated. Plasma does not separate from blood cells whilst circulating in the bloodstream because it is in a constant state of agitation.Chemical considerationsUpon exiting the body, bloodstains transit from bright red to dark brown, which is attributed to oxidation ofoxy-hemoglobin(HbO2) tomethemoglobin(met-Hb) andhemichrome(HC). The fractions of HbO2, met-Hb and HC in a bloodstain can used for age determination of bloodstains and can be measured by Reflectance Spectroscopy1. In vivohemoglobin molecules are mainly present in two forms: one without oxygen, de-oxyhemoglobin (Hb) and one saturated with oxygen, oxy-hemoglobin (HbO2), both have iron in the Fe2+state. HbO2can auto-oxidize into met-Hb, which contains iron in the Fe3+state. Met-Hb is incapable of binding oxygen. When met-Hb is formed in vivo it will be reduced back to Hb by reductase protein cytochrome b5, resulting in a small part (