Forensic Serology Questions and Answers

Answer: A

The key gives cat as the animal other than humans in which P30 occurs in seminal stain. P30 is the prostate specific antigen used in the test for semen, and it is found in the human seminal plasma. Fowl, rat and cow are not the keyed answer. The answer is A. P30 is a prostate protein, also known as prostate specific antigen, and tests for it are used to confirm that a stain contains seminal fluid. They are more specific than the acid phosphatase test, which also reacts with other fluids. The question asks for an animal in which P30 is also found, and the key gives the cat, so fowl, rat and cow are not the keyed answer.

Answer: B

The Davidson (Davidsohn) body is present in the neutrophil, the polymorphonuclear white cell. It is the small drumstick-like projection of the nucleus that represents the inactive X chromosome of a female and is the basis of sex identification from blood films. Basophils, lymphocytes and monocytes do not show it. So B is correct. Davidsohn body is another name for the nuclear appendage of the neutrophil that is also called a drumstick, and its presence in a small percentage of the neutrophils of a female blood film helps to tell female blood from male. The other white cells, namely the basophil, lymphocyte and monocyte, do not show such an appendage.

Answer: C

The key credits Roberts with devising the starch-iodine test for the presence of semen. Willott, E.M. Southern and Ouchterlony are known for other things: Southern for the Southern blot technique in DNA analysis, and Ouchterlony for the double diffusion method in immunology. The answer is C. The test gives a blue-black colour when iodine acts on starch, and it was proposed as a presumptive test for semen on the basis of the starch-iodine reaction. A presumptive test shows only that a stain may be semen and must be followed by a confirmatory test, such as demonstration of spermatozoa or the P30 test.

Answer: B

O-tolidine is 3,3'-dimethyl benzidine, so it is the dimethyl derivative of benzidine. Like benzidine it gives a blue colour with hydrogen peroxide in the presence of blood, which makes it useful for the presumptive test for blood.

Phenolphthalein, spelled Phenopthaline in the paper, is the reagent of the Kastle Meyer test and is a different compound. Sodium acetate and sodium chloride are simple salts and have no relation to a dimethyl biphenyl diamine.

Answer: D

Serum protein polymorphism is demonstrated by electrophoresis. Genetic variants of proteins such as haptoglobin, transferrin and group specific component differ in charge or size, so they migrate to different positions in an electric field and give different band patterns.

HPLC and GC-MS are used for small molecules such as drugs. Centrifugation separates components by density and cannot display variants of a single protein. Only electrophoresis separates the protein variants.

Answer: B

Electrophoresis is used to identify the enzymes in blood samples. Enzymes such as phosphoglucomutase, erythrocyte acid phosphatase and esterase D occur in several genetic forms, and these isoenzymes separate in a gel under an electric field and are stained to show the bands.

Southern blotting detects DNA sequences and Northern blotting detects RNA, so neither identifies an enzyme. TLC is used for small organic molecules such as drugs and dyes, not for the enzyme variants of blood.

Answer: C

Both statements are incorrect. In disputed paternity and maternity cases the blood group of the child can be determined and compared with that of the parents, so the assertion is wrong. The blood groups are inherited according to Mendel's laws, so the reason is also wrong, and it is this inheritance that makes blood grouping useful to exclude a parent.

The options that call either statement correct are wrong. Option B takes the reason as correct, option A takes both, and option D takes the assertion.

Answer: D

The key gives Ottenberg as the person who first applied ABO grouping in disputed paternity, around 1921. I could not check the date against a source, so the key is followed.

Landsteiner discovered the ABO groups in 1901 but did not apply them to paternity. Hirschfeld, with von Dungern, showed that the groups are inherited, a step that made the application possible. Bernstein later gave the three allele theory of ABO inheritance in 1924. These are earlier or later contributions, which the key does not take as the first use in paternity.

Answer: C

Genes that exist as alternative forms at the same locus on a chromosome are called alleles. For example, the A, B and O forms of the ABO gene are alleles at one locus on chromosome 9.

Loci is the plural of locus and refers to the positions, not to the forms. An antigen is a molecule that provokes an immune response. A phenotype is the observable expression of the genes, such as the blood group. Only allele names the alternative forms.

Answer: A

The official key says the detection of colostrum is essential in a case of concealment of birth. Colostrum is the thin yellowish fluid secreted by the breast in late pregnancy and in the first days after delivery, so finding it in a woman suspected of having delivered shows recent childbirth.

In rape the issue is semen or injury, in a paternity dispute it is blood groups or DNA, and in immigration it is age or identity. None of these depends on whether the woman has recently given birth.