Forensic Serology Questions and Answers

Answer: C

Both statements are incorrect, option (C). Not all human beings have A antigens in the blood: people of group O and group B have no A antigen on their red cells. So the assertion is false.

The reason is also false. A person does not make both anti-A and anti-B antibodies in general: a person of group A makes anti-B only, a person of group B makes anti-A only, and only group O makes both. Moreover, the antibodies are the result of the absence of an antigen, not the cause of having it. So (A), (B) and (D) are wrong.

Answer: A

Short fragments of DNA labelled with a radioactive tag are known as probes, option (A). A probe is a labelled piece of single-stranded DNA that binds to its complementary sequence, so it is used in techniques such as Southern blotting and DNA fingerprinting.

Primers are short pieces of DNA that start replication in PCR and are not usually described as radioactive tags. STRs (short tandem repeats) and SSRs (simple sequence repeats) are kinds of repeat sequence in DNA, not labelled fragments.

Answer: D

If one parent is of blood type A and the other is type B, the children can be AB, A, B or O, depending on whether each parent carries an O allele. The option that covers all the possibilities listed is therefore right.

AB alone, B alone or O alone would each leave out other possible outcomes, so no single option is complete. The listed types (AB, B, O) are all possible, hence 'all of the above'.

Answer: C

The correct match is a-iii, b-iv, c-ii, d-i. The alpha amylase test is for saliva, nuclear fast red is used to stain sperm heads, Brentamine fast blue B is the acid phosphatase reagent that detects seminal fluid, and thrombocytes are the platelets that take part in blood clotting.

The other codes give saliva to a wrong test or link thrombocytes with semen, which does not fit.

Each of these tests is used in the screening of body fluid stains at a crime scene.

Answer: B

Leukocytes, the white blood cells, are primarily involved in the immune system. They defend the body against infection and foreign matter.

The transport of oxygen is done by red blood cells carrying haemoglobin. The transport and removal of carbon dioxide is done mainly by plasma and red cells, so the other three options describe functions that are not those of leukocytes.

There are five types of leukocyte, including neutrophils and lymphocytes, and each has a part in defence.

A count of the white cells in the blood is used by doctors to find infection.

Answer: C

The protein markers found in human sperm are peptidase C and sperm diaphorase, the keyed pair. These are enzyme markers studied in forensic serology of seminal stains.

Amylase is the enzyme of saliva, and transferrin is a serum protein found in blood, so options containing a or c are wrong.

Seminal stains are examined with enzyme and protein markers because sperm may not be present in the sample.

Answer: A

Both statements are correct. Saliva is produced in the mouth and starts the digestion of food, and the reason is true because the enzyme alpha-amylase in it breaks down starch into sugars.

The second option calls both statements incorrect, and the third and fourth call one of them incorrect. Since both are accepted as true, the first option is the answer.

Starch digestion therefore begins in the mouth before the food reaches the stomach.

The same enzyme is used in the alpha amylase test on stains.

Answer: A

Both statements are correct. Blood flows more slowly than water because blood is more viscous, since it contains cells and proteins that increase internal friction.

The viscosity is the cause of the slower flow, so the reason supports the assertion. The options that call one or both incorrect contradict the physics of fluids.

The viscosity of blood is roughly three to four times that of water.

Viscosity is the property of a fluid that resists flow.

Answer: C

The Periodic Acid Schiff test is not a presumptive test for bloodstains. It detects carbohydrates such as glycogen and mucins and is used in histology.

Leucomalachite green, phenolphthalein (the Kastle-Meyer test) and tetramethylbenzidine are all presumptive tests for blood, which rely on the peroxidase-like activity of haemoglobin to produce a colour.

A positive presumptive test only suggests blood, and a confirmatory test is needed to prove it.