Forensic Serology Questions and Answers

Q: In seminal fluid, the amount of spermatozoa is :

Seminal fluid contains about 100 million spermatozoa per ml.A normal ejaculate of about 2 to 5 ml contains tens of millions of sperm per millilitre; the classic textbook figure is about 100 million per ml, and counts below about 15 million per ml are considered low.3 thousand per ml is far too few, and the figures per ounce and per pint (50 billion and 25 trillion) are wildly too high when converted to millilitres.

Q: Synthesis of DNA to mRNA is known as :

Synthesis of mRNA from DNA is transcription.In transcription, RNA polymerase reads a gene on the DNA template and builds a complementary messenger RNA molecule. This is the first step of gene expression.Translation is the next step, in which ribosomes read the mRNA to make a protein. 'Transportation' is not a stage of gene expression, and fertilization is the union of egg and sperm.

Q: PGM-I Enzyme 1-1 type is characterized by :

The PGM-1 type 1-1 is characterised by a and c bands.Phosphoglucomutase (PGM-1) is a polymorphic enzyme used in older forensic blood and semen typing. On electrophoresis, the PGM-1 type 1 shows the a and c bands, type 2 shows the b and d bands, and the heterozygote 2-1 shows all four bands, a, b, c and d.The 'a and b' and 'a and d' combinations do not match any standard phenotype, and 'a, b, c and d' is the 2-1 type.

Q: Which of the following is correct for the disadvantages of RFLP technqiue ?I. Takes a lot of timeII. Requires large intact sampleIII. Produces large (30,000 BP) DNA strand.

All three are disadvantages, so I, II and III are correct.RFLP analysis (restriction fragment length polymorphism) involves digesting DNA, separating the fragments on a gel, Southern blotting and probing, which takes days or weeks (I). It needs a relatively large amount of intact, high-molecular-weight DNA, so degraded samples often fail (II). And it works with long fragments, thousands to tens of thousands of base pairs, which are harder to resolve precisely than the short products used in modern STR typing (III).Since every statement is a drawback, the options with only two of them are incomplete.

Q: Venous blood collected as a reference blood sample should be collected in :

Reference blood should go in purple-topped vacutainer EDTA tubes.EDTA (ethylenediaminetetraacetic acid) is an anticoagulant that chelates calcium, which also inhibits the DNases that degrade DNA, so whole blood collected in EDTA is the standard reference sample for DNA profiling. Tubes containing EDTA are identified by a purple (lavender) stopper.Green tops contain heparin, which inhibits PCR, and yellow tops contain ACD or are used for blood cultures. Pink tops also hold EDTA but are used mainly in blood banking for cross-matching, so the standard forensic reference tube is the purple one.

Q: Which of the following is used to preserve DNA at room temperature?

DNA is preserved at room temperature on an FTA card.FTA cards (Flinders Technology Associates) are filter papers impregnated with chemicals that lyse cells, denature proteins and protect the released DNA from nucleases, bacteria and ultraviolet damage. Blood or buccal samples spotted on them stay stable for years at room temperature, which makes them convenient for reference samples and databases.Chelex is a resin used to extract DNA, and DNA IQ is a magnetic-bead extraction system; neither is a storage medium. Plain Whatman paper can hold a dried stain but lacks the chemicals that protect the DNA.

Q: In an individual lacking spermatozoa in the seminal stains, which test is most suitable for its identification among the following ?

The most suitable test is the seminal acid phosphatase test.In azoospermic or vasectomised men the semen contains no spermatozoa, so microscopic identification of sperm is impossible. The seminal fluid itself, however, still contains very high levels of acid phosphatase secreted by the prostate, and the acid phosphatase test detects it rapidly and with high sensitivity. It is the standard presumptive test for semen in such cases.The Florence (choline) and Barberio's (spermine picrate) tests are old crystal tests that are much less sensitive and specific. 'Semen specific test' is not the name of a recognised test.

Q: Among the following which is more suitable to determine the species origin of blood stains ?

The more suitable technique is cross-over electrophoresis.Species origin is determined by the reaction between proteins in the stain and an antiserum against a particular species. In cross-over (counter) immunoelectrophoresis, an electric field drives the antigen and antibody towards each other through a gel, so they meet and form a precipitin line quickly and with much greater sensitivity than when they diffuse on their own. It works on old and small stains and uses little antiserum.The precipitin tube (ring) test relies on the same reaction but is slower and less sensitive. Latex agglutination and the antiglobulin consumption test are used for other serological purposes, not as the method of choice for species identification.

Q: Brentamine Fast Blue-B is used to test :

Brentamine Fast Blue B is used to test seminal stains.It is the colour reagent of the acid phosphatase test. Seminal acid phosphatase cleaves a substrate such as alpha-naphthyl phosphate to release naphthol, which couples with Brentamine Fast Blue B to give an intense purple colour within seconds. The speed and intensity of the reaction indicate semen, which contains far more acid phosphatase than any other body fluid.Vaginal fluid has only low acid phosphatase activity and gives a slow, weak reaction. Saliva is identified by its amylase (starch-iodine or Phadebas tests) and urine by urea or creatinine tests.

51.

In seminal fluid, the amount of spermatozoa is :

A.3 thousand spermatozoa per ml
B.50 billion spermatozoa per ounce
C.25 trillion spermatozoa per pint
D.100 million spermatozoa per ml

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: D

Seminal fluid contains about 100 million spermatozoa per ml.

A normal ejaculate of about 2 to 5 ml contains tens of millions of sperm per millilitre; the classic textbook figure is about 100 million per ml, and counts below about 15 million per ml are considered low.

3 thousand per ml is far too few, and the figures per ounce and per pint (50 billion and 25 trillion) are wildly too high when converted to millilitres.

Discuss in Forum

52.

Synthesis of DNA to mRNA is known as :

A.Translation
B.Transportation
C.Fertilization
D.Transcription

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: D

Synthesis of mRNA from DNA is transcription.

In transcription, RNA polymerase reads a gene on the DNA template and builds a complementary messenger RNA molecule. This is the first step of gene expression.

Translation is the next step, in which ribosomes read the mRNA to make a protein. 'Transportation' is not a stage of gene expression, and fertilization is the union of egg and sperm.

Discuss in Forum

53.

PGM-I Enzyme 1-1 type is characterized by :

A.a and b bands
B.a and c bands
C.a and d bands
D.a, b, c and d bands

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

The PGM-1 type 1-1 is characterised by a and c bands.

Phosphoglucomutase (PGM-1) is a polymorphic enzyme used in older forensic blood and semen typing. On electrophoresis, the PGM-1 type 1 shows the a and c bands, type 2 shows the b and d bands, and the heterozygote 2-1 shows all four bands, a, b, c and d.

The 'a and b' and 'a and d' combinations do not match any standard phenotype, and 'a, b, c and d' is the 2-1 type.

Discuss in Forum

54.

Which of the following is correct for the disadvantages of RFLP technqiue ?

I. Takes a lot of time
II. Requires large intact sample
III. Produces large (30,000 BP) DNA strand.

A.I & II are correct
B.I & III are correct
C.II & III are correct
D.I, II & III are correct

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: D

All three are disadvantages, so I, II and III are correct.

RFLP analysis (restriction fragment length polymorphism) involves digesting DNA, separating the fragments on a gel, Southern blotting and probing, which takes days or weeks (I). It needs a relatively large amount of intact, high-molecular-weight DNA, so degraded samples often fail (II). And it works with long fragments, thousands to tens of thousands of base pairs, which are harder to resolve precisely than the short products used in modern STR typing (III).

Since every statement is a drawback, the options with only two of them are incomplete.

Discuss in Forum

55.

Proteins of plant origin (obtained from seed extracts) which behaves like antibody commonly termed as :

A.Agglutinogens
B.Lectins
C.Antisera
D.Plasma protein

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

Plant proteins from seed extracts that behave like antibodies are called lectins.

Lectins bind specific sugars on cell surfaces and can agglutinate red cells of particular blood groups, much as antibodies do. Examples are anti-H from Ulex europaeus and anti-A1 from Dolichos biflorus, both used in serology.

Agglutinogens are the antigens on red cells, not the reagents that react with them. Antisera are antibody-containing sera from animals or people, and plasma proteins come from blood, not from plants.

Discuss in Forum

56.

Venous blood collected as a reference blood sample should be collected in :

A.Pink-topped vacutainer EDTA tubes
B.Purple-topped vacutainer EDTA tubes
C.Green-topped vacutainer EDTA tubes
D.Yellow-topped vacutainer EDTA tubes

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

Reference blood should go in purple-topped vacutainer EDTA tubes.

EDTA (ethylenediaminetetraacetic acid) is an anticoagulant that chelates calcium, which also inhibits the DNases that degrade DNA, so whole blood collected in EDTA is the standard reference sample for DNA profiling. Tubes containing EDTA are identified by a purple (lavender) stopper.

Green tops contain heparin, which inhibits PCR, and yellow tops contain ACD or are used for blood cultures. Pink tops also hold EDTA but are used mainly in blood banking for cross-matching, so the standard forensic reference tube is the purple one.

Discuss in Forum

57.

Which of the following is used to preserve DNA at room temperature?

A.FTA Card
B.Chelex
C.DNAIQ
D.Whatman's paper

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

DNA is preserved at room temperature on an FTA card.

FTA cards (Flinders Technology Associates) are filter papers impregnated with chemicals that lyse cells, denature proteins and protect the released DNA from nucleases, bacteria and ultraviolet damage. Blood or buccal samples spotted on them stay stable for years at room temperature, which makes them convenient for reference samples and databases.

Chelex is a resin used to extract DNA, and DNA IQ is a magnetic-bead extraction system; neither is a storage medium. Plain Whatman paper can hold a dried stain but lacks the chemicals that protect the DNA.

Discuss in Forum

58.

In an individual lacking spermatozoa in the seminal stains, which test is most suitable for its identification among the following ?

A.Seminal acid phosphatase test
B.Choline test
C.Semen specific test
D.Barberio's test

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

The most suitable test is the seminal acid phosphatase test.

In azoospermic or vasectomised men the semen contains no spermatozoa, so microscopic identification of sperm is impossible. The seminal fluid itself, however, still contains very high levels of acid phosphatase secreted by the prostate, and the acid phosphatase test detects it rapidly and with high sensitivity. It is the standard presumptive test for semen in such cases.

The Florence (choline) and Barberio's (spermine picrate) tests are old crystal tests that are much less sensitive and specific. 'Semen specific test' is not the name of a recognised test.

Discuss in Forum

59.

Among the following which is more suitable to determine the species origin of blood stains ?

A.Precipitin tube technique
B.Crose-over electrophoresis
C.Latex agglutinins
D.Anti-globulin consumption test

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

The more suitable technique is cross-over electrophoresis.

Species origin is determined by the reaction between proteins in the stain and an antiserum against a particular species. In cross-over (counter) immunoelectrophoresis, an electric field drives the antigen and antibody towards each other through a gel, so they meet and form a precipitin line quickly and with much greater sensitivity than when they diffuse on their own. It works on old and small stains and uses little antiserum.

The precipitin tube (ring) test relies on the same reaction but is slower and less sensitive. Latex agglutination and the antiglobulin consumption test are used for other serological purposes, not as the method of choice for species identification.

Discuss in Forum

60.

Brentamine Fast Blue-B is used to test :

A.Seminal stains
B.Vaginal stains
C.Saliva stains
D.Urine stains

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

Brentamine Fast Blue B is used to test seminal stains.

It is the colour reagent of the acid phosphatase test. Seminal acid phosphatase cleaves a substrate such as alpha-naphthyl phosphate to release naphthol, which couples with Brentamine Fast Blue B to give an intense purple colour within seconds. The speed and intensity of the reaction indicate semen, which contains far more acid phosphatase than any other body fluid.

Vaginal fluid has only low acid phosphatase activity and gives a slow, weak reaction. Saliva is identified by its amylase (starch-iodine or Phadebas tests) and urine by urea or creatinine tests.

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