Forensic Serology Questions and Answers

Answer: B

A thermal cycler is used in the amplification of DNA.

The polymerase chain reaction copies a target DNA sequence through repeated cycles of denaturation (about 94-95°C), annealing of primers (about 50-65°C) and extension (about 72°C). A thermal cycler changes the temperature of the reaction tubes through these steps automatically, doubling the target with each cycle. Forensic STR profiling depends on this amplification.

Detection of blood or semen stains uses presumptive and confirmatory tests, and plasma is separated from blood by centrifugation, not by a thermal cycler.

Answer: B

They are phytoagglutinins (lectins).

Some plant seeds contain proteins that bind specific sugars on red cells and agglutinate them, much as antibodies do. Examples are the lectin of Dolichos biflorus, which reacts with A1 cells, and that of Ulex europaeus, which reacts with the H antigen. They are used as blood grouping reagents.

Agglutinogens and antigens are the substances on red cells that are agglutinated, not plant proteins. Antibodies are made by the immune system of animals, so plant proteins behaving like them are given the separate name phytoagglutinins.

Answer: C

The one that is not a red cell enzyme is haptoglobin.

Haptoglobin is a plasma (serum) protein, an alpha-2 globulin that binds free haemoglobin. It is a classic serum protein marker in forensic serology, with types Hp 1-1, 2-1 and 2-2, but it is not an enzyme and not found inside red cells.

Phosphoglucomutase (PGM) and adenylate kinase (printed 'Adrylate kinase') are polymorphic enzymes of red cells used in stain typing before DNA methods, and red cells also contain peroxidase activity, such as glutathione peroxidase.

Answer: B

Nuclear DNA is usually found in pulled hair.

A hair pulled out forcibly in the growing (anagen) phase brings its root and the surrounding root sheath cells with it, and these living cells contain nuclei. That makes pulled hairs a good source of nuclear DNA for STR profiling.

Shed hairs are in the resting (telogen) phase and have a club root with few or no cells. Cut hair consists only of the keratinised shaft, which has no nuclei, and singeing destroys the DNA further. These are usually analysed for mitochondrial DNA instead.

Answer: C

Spermine is detected by the Barberio test.

In Barberio's test a saturated solution of picric acid is added to a semen extract; spermine forms yellow needle-shaped crystals of spermine picrate, seen under the microscope. It is a classic presumptive test for semen.

The Florence test detects choline, giving brown crystals with iodine in potassium iodide. Fluorescence (under UV light) helps locate stains, ELISA is used for semen-specific proteins such as PSA, and agglutination inhibition is a blood or secretor grouping method. None of these is the spermine test.

Answer: D

The cells not useful for DNA analysis are erythrocytes.

Mature human red blood cells lose their nucleus during development, so they contain no nuclear DNA. The DNA typed from a blood stain comes from the white blood cells (leucocytes) in it.

Vaginal epithelial cells, buccal (cheek) cells and spermatozoa all have nuclei and are routine sources of DNA. Buccal swabs are the standard reference sample, and differential extraction separates sperm DNA from vaginal cell DNA in sexual assault cases.

Answer: A

The first Serology Department of the Government of India was set up in 1910.

It began in Calcutta as the office of the Imperial Serologist to the Government of India, created to test bloodstains sent in criminal cases, and it is the forerunner of the present Serologist and Chemical Examiner's laboratory. It came after the Chemical Examiner's laboratories of the nineteenth century and the Calcutta fingerprint bureau of 1897.

The later dates do not mark its foundation: 1915 and 1925 fall after the department was already working, and 1947 is the year of Independence, not of any forensic institution's founding.

Answer: B

The International Association of Bloodstain Pattern Analysts was formed in 1983.

It grew out of the bloodstain pattern courses taught by Herbert MacDonell in the 1970s, whose students founded the association to set standards, share research and train analysts. It publishes a journal and holds annual training conferences.

1972 is too early, when bloodstain pattern training was only beginning, and 1985 and 1989 are after the association was founded.

Answer: B

The DNA profile database is CODIS.

CODIS, the Combined DNA Index System, is the FBI's software and database linking DNA profiles at local, state and national levels. An analyst searches a profile from a crime scene against the indexes of offenders, arrestees and forensic unknowns to find a match.

PCR, the polymerase chain reaction, is the technique that copies DNA, not a database. AFIS is the fingerprint database, and PDQ (Paint Data Query) is the RCMP's database of automotive paint.

Answer: C

IgM is the better activator of complement because of its pentavalent structure.

The classical pathway starts when C1q binds to at least two antibody Fc regions close together on an antigen. IgM is a pentamer of five antibody units joined by a J chain, so a single molecule bound to a cell surface already offers several Fc regions to C1q. IgG is a monomer, and two IgG molecules must happen to bind next to each other to do the same.

IgM has a much higher molecular weight than IgG (about 900 kDa against 150 kDa), not a lower one, and lower concentration would make it less effective, not more. The secretory form is a feature of IgA and has nothing to do with complement activation.