Forensic Serology Questions and Answers

Answer: C

The correct matching is P30 with semen, creatine with urine, ptyaline with saliva and PGM with blood. P30 is the prostate specific antigen used to detect semen, creatine or creatinine is a urinary constituent, ptyalin is the salivary amylase, and PGM, phosphoglucomutase, is the enzyme typed in bloodstains. This is code C, (iv) (iii) (ii) (i).

Option A gives ptyalin to blood. Option B gives P30 to urine. Option D matches in the printed order and so makes P30 a blood marker, which is wrong.

Answer: D

The radial diffusion test is used for the detection of amylase. The sample is put in a well in a gel with starch, and amylase diffuses out and digests the starch, which is shown by iodine as a clear ring whose diameter shows the amount. It is used for saliva stains.

Colostrum, haptoglobin and haemoglobin are identified by other tests, such as precipitin tests or immunological methods. Radial diffusion with starch fits only the enzyme amylase.

Answer: B

In the starch iodine test the starch turns blue on addition of iodine, a deep blue black colour, because iodine enters the helix of the amylose in starch and forms a complex. It is used as a test for starch and, indirectly, for amylase in saliva.

Purple, green and pink are not the colours of this complex. A purple colour is shown by iodine in a non polar solvent, which should not be confused with the starch complex.

Answer: A

The maintenance of the correct number of chromosomes in mitosis depends on the duplication of DNA, option A. Before a cell divides the DNA is copied once, so that each daughter cell gets a complete set, and the number of chromosomes is kept the same. DNA mutation (B) is a change in the sequence, which does not keep the number correct, and a single nucleotide polymorphism (C) is a variation at one base position between individuals. Since only duplication is the process that does so, option D, all of the above, is also rejected. The DNA is duplicated in the S phase of the cell cycle, and the copies are then pulled apart equally to the two daughter cells during mitosis.

Answer: B

Transferrin is not a red cell isoenzyme, option B. Transferrin is a serum protein that carries iron in the plasma, and it is typed as a protein polymorphism of the serum. Adenosine deaminase, glutamate pyruvate transaminase and phosphoglucomutase are all enzymes found in the red cells that show genetic variants, and they are used in forensic typing of blood stains. So A, C and D are red cell isoenzymes and B is the one that is not.

Answer: A

The white blood cells are involved in the immune system of the human body, option A. Lymphocytes, neutrophils, monocytes and the other leucocytes recognise and destroy foreign organisms and make antibodies. The red cells (B) carry oxygen, the thrombocytes, or platelets (C), take part in clotting, and serum (D) is the fluid left after clotting, which contains antibodies but is not itself a cell of the defence system, so the key takes the white cells as the answer. The white cells include the lymphocytes, which make antibodies and carry out cell-mediated immunity, and the phagocytes, which engulf foreign particles.

Answer: D

Southern blotting is not a step in the polymerase chain reaction, option D. PCR copies a region of DNA by repeated cycles of denaturation, in which the strands are separated by heat, annealing, in which primers bind to the single strands, and extension, in which the polymerase adds nucleotides. Southern blotting is a separate method to detect a specific DNA sequence after electrophoresis and transfer to a membrane. Annealing (A) and extension (C) are steps of PCR, and the item printed as Deuaturation (B) is the denaturation step. A PCR run usually has about thirty cycles, and each cycle roughly doubles the amount of the target DNA, so that a few copies can be made into millions.

Answer: A

Both statements are correct, option A. At the scene of an offence, a detailed note should be made of the amount of blood found or splattered, since the quantity of blood loss is part of the reconstruction of events. The reason is also correct: the amount of bleeding helps in judging how long the victim survived after the assault, because a large pool of blood suggests that the heart went on beating for some time. Option B calls the reason incorrect, option C the assertion, and option D both, which would deny a recognised point in crime scene investigation.

Answer: B

Vaginal secretion contains Doderlein's bacilli, option B. These are lactobacilli that live in the normal vagina and produce lactic acid, which keeps the secretion acidic, and their presence is used in the examination of vaginal swabs. Urea (A) is a constituent of urine and sweat, glyoxalase I (C) is an enzyme of the red cells that is used in the typing of blood, and serum cholinesterase (D) is a plasma enzyme. Glyoxalase I is a red cell enzyme used in blood grouping, and serum cholinesterase is an enzyme of the plasma, so neither is a normal constituent of the vaginal secretion in the sense used here.

Answer: B

The key gives P30, option B, as the thing detected by counter immuno electrophoresis in this question. P30 is the prostate specific antigen found in semen, and CIEP is a quick precipitin test in which the antigen and antibody move toward each other in an electric field and form a visible line, and it is used for the identification of seminal stains. It is not used for DNA (A), and the key does not accept the general term protein (C) or isoenzymes (D).