Forensic Serology Questions and Answers

Answer: D

Blood in the semen is called hematospermia.

Hematospermia has several causes, including infections and injury, and in a legal case its presence in a stain can be linked to bleeding of the genital tract.

The word combines blood (haema) and semen (sperma). The pink or reddish colour is due to the blood.

Azoospermia is no sperm in the semen, oligospermia is a low sperm count, and histospermia is not the term for blood in semen. So those options are wrong.

Answer: A

The double helix structure was reported by Watson and Crick.

The discovery explained how the genetic information is stored and copied, and it is the basis of the later development of DNA profiling.

James Watson and Francis Crick published the structure in 1953, using the X-ray diffraction work of Rosalind Franklin and Maurice Wilkins.

Saiki and Mullis are linked with PCR, Oswald Avery showed that DNA is the genetic material, and Alec Jeffreys developed DNA fingerprinting. They did not report the double helix.

Answer: A

Such individuals are called secretors.

The secretor status is controlled by a gene, and it is useful in forensic work because blood group can be found from saliva or semen stains of secretors.

About four in five people secrete their A, B and H blood group substances in saliva, semen and other body fluids, so the group can be found from those fluids. They are called secretors.

Non-secretors do not secrete the substances in fluids, and Lewis positive and Lewis negative refer to another blood group system, so they are not the term asked.

Answer: A

In STR loci the tandem repeat unit consists of 2-7 bp.

STR loci are amplified by PCR, and the lengths of the products, which depend on the number of repeats, are compared between samples.

Short tandem repeats are short sequences of two to seven base pairs repeated in tandem, and the number of repeats varies between people, which makes them useful in DNA profiling.

Units of 242 bp, 1100 bp or 35 bp are too long for short tandem repeats. Repeats of about 35 bp are in the larger VNTR class.

Answer: C

Prostate-specific antigen is also called P30.

A test for PSA is a good indication of semen, and it works even if there are no spermatozoa, as in the case of a man who has had a vasectomy.

The protein, a glycoprotein made in the prostate, has a molecular weight of about 30,000 and is hence known as P30. It is a marker for the presence of seminal fluid.

Proteinase K is an enzyme used in DNA extraction, amylase is an enzyme found in saliva, and ptylase is a term for salivary amylase. They are not names of PSA.

Answer: B

Seminal acid phosphatase is produced in the prostate gland.

The acid phosphatase test is rapid, and a positive reaction is only presumptive, and it needs to be followed by tests like those for PSA or sperm.

The prostate secretes a fluid rich in acid phosphatase that forms part of the seminal fluid, and its high level in a stain is used as a presumptive test for semen.

The adrenal, thyroid and pituitary glands are endocrine glands that do not contribute the enzyme to semen.

Answer: B

In SDS-PAGE the role of SDS is to denature proteins.

Sodium dodecyl sulphate unfolds the proteins and coats them with negative charge in proportion to their length, so that they migrate through the polyacrylamide gel by size alone and not by their own shape or charge. It binds to the proteins in doing so, but the purpose is the denaturation and uniform charge.

SDS does not identify or isolate the proteins, which is done by comparison with markers and by later steps.

Answer: C

Rocket immunoelectrophoresis is also known as the Laurell technique.

Carl-Bertil Laurell developed it in 1966. An antigen is run electrophoretically into agarose gel containing antibody, and a rocket-shaped precipitate forms whose height is proportional to the amount of antigen.

Immunodiffusion and the ring test rely on diffusion and not on an electric field, and crossed-over electrophoresis is a different counter-current method.

Answer: C

The most reliable test for semen in the absence of spermatozoa is prostate specific antigen (p30).

PSA is made by the prostate and is present in seminal plasma even when the man is azoospermic or has had a vasectomy, and it is very specific to semen, so it is used as a confirmatory test.

Acid phosphatase and esterase are presumptive and can be found in other fluids, and the Florence test is a crystal test that is less reliable and gives false results.

Answer: D

The test that is not a catalytic colour test for blood is Teichmann's test.

Teichmann's test is a crystal test in which haemin crystals form on heating blood with glacial acetic acid and a chloride. O-tolidine, tetramethylbenzidine and Adler's benzidine test are catalytic tests, in which the peroxidase-like action of haemoglobin gives a colour with hydrogen peroxide.

Hence only Teichmann's test is outside the group.