Forensic Serology Questions and Answers

Answer: B

ABO antigens are present on the surface of the red blood cells (RBC). The A and B antigens are carbohydrate groups attached to proteins and lipids in the membrane, and the matching antibodies are in the serum. White cells do carry other antigens (HLA), but the ABO antigens are classically described on red cells, and the nucleus and cytoplasm do not display them on their surface. Option B is correct.

Answer: D

Human seminal fluid contains about 100 million spermatozoa per millilitre, which is option D. A normal count is at least 15 to 20 million per millilitre, and typical healthy values run to tens or hundreds of millions. The other figures, 3 thousand per ml, 50 billion per ounce and 25 trillion per pint, are not consistent with the normal count. For comparison, 100 million per ml is roughly 3 billion per ounce.

Answer: C

Different forms of the same gene or marker are called alleles. An allele is one of the alternative versions of a gene found at the same position on a chromosome, such as the A, B and O alleles of the blood group gene. Genetic linkage is the tendency of genes close together on a chromosome to be inherited together, linkage equilibrium describes random association between alleles at different loci, and the locus is the position itself. Option C is correct.

Answer: C

Esterase-D is visualised with 4-methyl umbelliferyl acetate. The enzyme splits this substrate to release the fluorescent 4-methyl umbelliferone, which shows as a bright band under ultraviolet light on the gel. Glycine-sodium carbonate solution is a buffer used to stop or enhance the fluorescence, glucose-1-phosphate is a substrate for phosphoglucomutase, and reduced glutathione is a substrate for glyoxalase I. Option C is correct.

Answer: C

The locus used to determine both male and female gender in DNA fingerprinting is amelogenin. The amelogenin gene is on both X and Y chromosomes, in a form that gives a different fragment size on each, so a female gives a single X band and a male gives both X and Y bands. DYS19 and DYS393 are loci on the Y chromosome only, so they give a result only for a male, and a Y-plex ladder is a size marker, not a locus. Option C is correct.

Answer: A

The Jaffe test is a reaction between creatinine and picric acid, option (A). In an alkaline solution the creatinine in urine or serum forms a red-orange coloured complex with picric acid, which is used for the colorimetric estimation of creatinine. Urea does not give this colour, so options with urea, (B) and (C), are wrong, and ammonium hydroxide is not the reagent, so (D) is wrong. The orange-red colour is read at about 500 nm and the method is simple, which is why it was in use for a long time in laboratories.

Answer: B

The pigment found in faecal matter is urobilinogen, option (B), a colourless product of the breakdown of bilirubin by the gut bacteria, which is turned in the air to the brown pigments, with stercobilin as the end product, that give faeces their colour. Titanium oxide is a white mineral pigment of paints, creatinine is a waste product found in urine, and keratin is the protein of hair and nails, so (A), (C) and (D) are not pigments of faeces. Stercobilin is the pigment that is chiefly responsible for the brown colour, and a stool without it, as in an obstruction of the bile duct, is pale.

Answer: A

Vaginal secretions can be characterised on the basis of glycogenated epithelial cells, option (A), as the vaginal epithelium of the woman of reproductive age is rich in glycogen, and the cells stain with iodine to give a mahogany brown colour, which helps to tell vaginal material from other body fluids on a stain. Papillary, squamous and elongated cells are not specific in the same way, since squamous cells occur in many body sites, so (B), (C) and (D) are less suitable.

Answer: C

Colostrum in milk is indicative of recent delivery, option (C). It is the thin yellowish fluid, rich in protein, antibodies and fat globules, that the breast gives out in late pregnancy and during the first days after childbirth, before the true milk comes. Its presence in a woman is used in medical jurisprudence to show that she has delivered recently. Ovarian and uterine tumours do not cause it, and false pregnancy may cause secretion of milk but not typical colostrum, so (A), (B) and (D) are wrong. The secretion in the breast starts to change to mature milk by the third to fifth day after delivery.

Answer: A

The precipitin test is performed to determine the species of origin, option (A), of a blood stain or other protein material. An anti-serum made in a rabbit against human protein is layered with the extract of the stain, and a white ring of precipitate forms where the antigen and antibody meet if the stain is human. The test does not show the sex or the age of the person, so (B), (C) and (D) are wrong.