FRSC1030 Foundations in Forensic Science Chapter 9

Key Terms from chapter 9

Acid phosphatase (AP)

A class of enzymes that can catalyze chemical reactions of certain organic phophates, including seminal acid phosphatase (SAP), found in human semen at higher levels than in other body fluids, which makes it an ideal target for presumptive testing.

Agglutination

The clumping together of cells, particles, or molecules, most commonly seen in the context of antibody-antigen reactions. Incompatible blood types cause red blood cell agglutination due to the reactions between antigens on the RBCs and the antibodies in the plasma.

Alternate light source (ALS)

Use specific wavelengths of light to visualize evidence invisible to the naked eye, such as bodily fluids, trace evidence, and certain injuries. By illuminating evidence with a high-intensity light (such as UV light) and using barrier filters, investigators can cause substances to fluoresce or absorbe light differently, improving visualization, photography, and evidence collection.

Amylase

An enzyme found in saliva, used to digest starches, at higher levels than other bodily fluids, which makes it a good target for presumptive testing. 

Azoospermia

A condition in which the semen lacks spermatozoa (sperm cells), its principal cellular component, which means the usual method of staining sperm cells to test for semen would not work.

Background sample

A type of control sample used in presumptive testing, a sample collected from a reference area for comparison with samples collected on site.

Catalyst

A substance or chemical that speeds up a chemical reaction by lowering its activation energy but is not consumed.

Christmas tree stain

A common staining technique used to assist in visualizing sperm cells, in which the nucleus of the cell stains red and the tail portion becomes green.

Chemiluminescence

A phenomenon where a product of a reaction is the emission of light.

False negative

A negative result when there is actually some substance present

False positive

A positive result when there is no actual substance present

Field test

Also known as a presumptive test, or screening, an inexpensive, easy to use, and fast test done at the crime scene to quickly identify a piece of evidence such as blood. A positive result allows the examiner to presume the fluid is present, while a negative result quickly discards the evidence from needing further consideration.

Fluorescence

The emission of light by a substance that has absorbed and re-emitted it, typically at a longer wavelength, used for visualization enhancement, especially for fingerprints and biological samples.

Forensic serology

The study, detection, identification, and classification of bodily fluids in a legal setting, such as blood, semen, and saliva, and using DNA analysis to link evidence to individuals.

Genetic marker system

Systems that use genetic markers, genes or DNA sequences with known locations on a chromosome, to track the inheritence of characteristics or identify individuals

Genotype

The set of genes responsible for the phenotype of a person, the organism’s complete set of genetic material, or, more specifically, the two alleles that an individual carries for a particular gene

Hemastix

A field test used by many laboratories, particularly at crime scenes when containers of solutions can be hazardous, consisting of a plastic strip with a reagent-treated filter tab, used to detect the presence of blood.

Heme group

A ring-shaped iron-containing molecule that serves as an essential component of many proteins, including hemoglobin, myoglobin, and enzymes. It’s critical for a variety of biological functions, like oxygen transport, cellular respiration, and detoxification.

Hemoglobin

A protein in red blood cells containing iron that transports oxygen from the lungs to the rest of the body, and carries carbon dioxide waste back to the lungs. It’s a common target for blood testing because it’s present in high concentrations, is stable, and isn’t present in other bodily fluids.

Heterozygous

Having two different alleles of the same gene, one inherited from each parent. In a heterozygous genotype, an individual possesses two distinct versions of a gene at a particular locus on their chromosomes.

Homozygous

Having two identical alleles for a specific gene, one from each parent. 

Immunochromatography

A technique used in disposable devices that detect diseases by dropping a sample containing an analyte onto a test strip. The conjugated zones of the test strip contains antigens or antibodies, depending on the test, labeled with a compound that will make them visible, such as dye. The test and control lines contain antigens or antibodies that will bind selectively to the target and the unreacted labeled antibodies.

Kastle-Meyer test

A common presumptive test to detect the presence of blood, which relies on the peroxidase activity of hemoglobin to oxidize phenolphthalin into a bright pink colour.

Luminol test

A presumptive test that invloves spraying a chemical mixture on a suspected bloodstained area and observing the result, often in a darkened area. No UV light is required, the heme group from hemoglobin catalyzes the chemical reaction, which produces light as a result.

Phadebas test

A presumptive test used to detect saliva, using a moistened surface, like filter paper, against the surface of interest. The filter paper is treated with a colour-generating reagent, including starches bound to a dye molecule. When amylase is present, it catalyzes the separation of the dye molecule from the starch, resulting in a blue colour.

Phenolphthalein

An acid-base indicator that produces a bright pink colour when used in testing suspected blood. It gets oxidized by peroxide in the presence of hemoglobin.

Phenotype

The outward physical expression of inherited characteristics, or of the genotype.

Polymorphic

Having or occuring in many different forms, in particular in reference to species or genetic variation.

Product rule

A technique that will provide a random match probability when calculating a specific combination of traits, such as blood types and different isoenzyme systems.

Prostate-specific antigen (PSA)

An antigen used to detect prostate cancer in men, and is a target for forensic tests that use immunochromatography to screen for semen at a crime scene.

Presumptive test

Also known as a field test, or screening, an inexpensive, easy to use, and fast test done at the crime scene to quickly identify a piece of evidence such as blood. A positive result allows the examiner to presume the fluid is present, while a negative result quickly discards the evidence from needing further consideration.

Random match probability

The statistical probability that a randomly selected person from a given population would have the same DNA profile as a suspect or a crime scene sample. Calculated by multiplying the frequencies of each allele at multiple DNA markers, a very low RMP indicates a strong likelyhood that a DNA match is not a coincidence.

Screening test

Also known as a presumptive or field test, an inexpensive, easy to use, and fast test done at the crime scene to quickly identify a piece of evidence such as blood. A positive result allows the examiner to presume the fluid is present, while a negative result quickly discards the evidence from needing further consideration.

Semen / seminal fluid

A semifluid mixture of cells, amino acids, sugars, salts, ions, and other organic and inorganic materials. 

Serology

The study of serum and other bodily fluids, especially in regard to the response of the immune system to pathogens or introduced substances

Spermatozoa

The principal cellular component of semen, also called sperm cell.

Tetramethylbenzidine

The reagent used in Hemastix tests when assessing a crime scene for blood.

True negative

A negative result provided by a test, when it is known that there is none of the specific substance present.

True positive

A positive result provided by a test, when it is known that there is some of the specific substance present.