Identification: Y-chromosome STR typing: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Identification: Y-chromosome STR typing

Sample item

A vaginal swab from an alleged assault contains a large quantity of the survivor's DNA and only a trace of male DNA, and routine autosomal STR typing fails to give a male profile. Which technique is most useful?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Y-chromosome STR typing

Y-STR typing amplifies only markers on the Y chromosome, so female DNA in excess does not interfere and a male haplotype can be obtained. Because the Y chromosome is passed unchanged along the paternal line, it cannot discriminate between paternally related males.

Option by option

  • A. Mitochondrial DNA sequencing

    Mitochondrial DNA is maternally inherited, and the survivor's own mitochondrial DNA would swamp the sample, so it does not identify the male.

  • B. Y-chromosome STR typing (correct)

    Y-STR targets male-specific DNA and works despite excess female DNA.

  • C. Blood grouping of the mixed stain

    ABO grouping of a mixed stain is not individualising and can be confounded by the survivor's blood group.

  • D. Microscopic hair comparison

    Microscopic hair comparison is non-specific and does not address trace male DNA in a swab.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is B, Y-chromosome STR typing. Y-STR typing amplifies only markers on the Y chromosome, so female DNA in excess does not interfere and a male haplotype can be obtained.

Why is "Mitochondrial DNA sequencing" not the answer?

Mitochondrial DNA is maternally inherited, and the survivor's own mitochondrial DNA would swamp the sample, so it does not identify the male.

Why is "Blood grouping of the mixed stain" not the answer?

ABO grouping of a mixed stain is not individualising and can be confounded by the survivor's blood group.

Why is "Microscopic hair comparison" not the answer?

Microscopic hair comparison is non-specific and does not address trace male DNA in a swab.

What concept does this question test?

It tests Identification: Y-chromosome STR typing in Forensic Medicine. Because the Y chromosome is passed unchanged along the paternal line, it cannot discriminate between paternally related males.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Identification: Y-chromosome STR typing?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.