Identification: limits of Y-STR matches: 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: limits of Y-STR matches

Sample item

A Y-chromosome STR profile from a stain at a crime scene matches the suspect. The suspect has a father and three brothers. What follows?

AThe match is as individualising as an autosomal STR profileBThe match excludes his brothers by recombinationCThe match shows the maternal lineage of the donorDThe match does not exclude his paternal male relatives

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

The answer and the reasoning

D. The match does not exclude his paternal male relatives

The Y chromosome passes unchanged from father to son, apart from rare mutations, so all paternally related men share the same haplotype. A Y-STR match therefore narrows the source to a paternal lineage but cannot single out one man. Autosomal STRs are needed for individualisation.

Option by option

A. The match is as individualising as an autosomal STR profile
Y-STR typing is less discriminating than autosomal typing for this reason.
B. The match excludes his brothers by recombination
The Y chromosome does not recombine in the male line, so brothers are not excluded.
C. The match shows the maternal lineage of the donor
The maternal lineage is traced by mitochondrial DNA, not by the Y chromosome.
D. The match does not exclude his paternal male relatives (correct)
Correct. Paternal relatives share the same Y haplotype.

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.

Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, The match does not exclude his paternal male relatives. The Y chromosome passes unchanged from father to son, apart from rare mutations, so all paternally related men share the same haplotype.

Why is "The match is as individualising as an autosomal STR profile" not the answer?

Y-STR typing is less discriminating than autosomal typing for this reason.

Why is "The match excludes his brothers by recombination" not the answer?

The Y chromosome does not recombine in the male line, so brothers are not excluded.

Why is "The match shows the maternal lineage of the donor" not the answer?

The maternal lineage is traced by mitochondrial DNA, not by the Y chromosome.

What concept does this question test?

It tests Identification: limits of Y-STR matches in Forensic Medicine. A Y-STR match therefore narrows the source to a paternal lineage but cannot single out one man. Autosomal STRs are needed for individualisation.

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: limits of Y-STR matches?

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.