Forensic Serology Questions and Answers

Answer: D

A chromosome consists of two arms (chromatids) made mainly of DNA and joined at the centromere. A gene is only a short stretch of DNA on a chromosome, a cell is the whole structural unit that contains the chromosomes, and a protein is a different kind of molecule. Hence the structure described is a chromosome.

Answer: A

The correct matching is cast off with linear (iii), drip with satellite (iv), swipe with stroke (ii) and arterial gushing with arc (i). A cast-off pattern forms a linear trail as blood is flung from a moving object, a drip leaves a round stain with small satellite spatters, a swipe is a smear or stroke, and an arterial spurt leaves arcs. So iii, iv, ii, i is right and the other combinations misplace at least two pairs.

Answer: B

The age of a bloodstain can be estimated from the change in colour (red to brown to black), from the globulin to albumin ratio and from changes in the protein pattern as the stain ages. DNA is a stable molecule that identifies who the blood came from, and it does not give a reliable measure of how old a stain is, so it is the exception in this question. The keyed answer is therefore DNA.

Answer: C

The double helical structure of DNA was reported in 1953 by Francis Crick and James Watson, who built on the X-ray work of Rosalind Franklin and Maurice Wilkins. Alec Jeffreys discovered DNA fingerprinting in 1984, E.M. Southern devised the Southern blot technique and Muller showed that X-rays cause mutations. So Crick and Watson is correct.

Answer: D

Humans have three major pairs of salivary glands, the parotid, the sublingual and the submandibular glands, together with many small minor glands. All of the glands listed are salivary glands found in humans, so the answer is 'All of the above'. Any single option would leave out two correct glands.

Answer: A

The lateral flow immunochromatographic strip test and the Rapid Stain Identification (RSID) kit detect human salivary amylase with antibodies, so they are confirmatory tests for human saliva. The Phadebas test shows amylase activity, but it is only a presumptive test because amylase is found in other fluids as well. UV examination is only a screening aid, so (i) and (ii) are correct.

Answer: C

Buccal epithelial cells come from the lining of the cheek and mouth, and they are shed into the saliva, so their presence confirms saliva. Semen is identified by spermatozoa or P30, blood by haemoglobin tests, and urine by urea and creatinine. So saliva is the correct answer.

Answer: C

The Assertion is correct: P30 (prostate specific antigen) is a seminal protein whose presence confirms a seminal stain. The Reason is wrong, because P30 is secreted by the prostate gland and not by Cowper's gland, which produces the pre-ejaculatory fluid. Hence (A) is correct but (R) is incorrect. The option saying both are correct overlooks the wrong gland, and the other two options wrongly reject (A).

Answer: A

In spermatogenesis a primary spermatocyte divides by the first meiotic division into two secondary spermatocytes, and each secondary spermatocyte divides in the second meiotic division into two spermatids. The spermatids then mature into spermatozoa by spermiogenesis. So the secondary spermatocyte gives rise to spermatids, not to primary spermatocytes, spermatogonia or spermatozoa directly.

Answer: C

The solvent system given as most suitable for chromatography of a blood sample is methanol, acetic acid and water in the ratio 90 : 3 : 7. Blood contains polar substances such as proteins and pigments, which need a polar solvent mixture with a little acid to run as compact spots. The other mixtures listed are either much less polar, as in chloroform with ethanol, or are different proportions of polar solvents, such as 70 : 30 methanol and water with no acid or ethanol with acetic acid and water at 92 : 1 : 7. Of the four, only option C has both the strongly polar methanol and water base and a small, acidic share of acetic acid, so it is the keyed answer.