Identification: STR profile in paternity testing: 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: STR profile in paternity testing

Sample item

At one STR locus a child has alleles 9 and 11, the mother has 9 and 10, and the alleged father has 11 and 13. Which statement is correct for this locus?

AThe obligate paternal allele is 10, which the alleged father lacksBThe obligate paternal allele is 9, which the alleged father lacksCThe obligate paternal allele is 13, which the child lacksDThe obligate paternal allele is 11, which the alleged father carries

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

The answer and the reasoning

D. The obligate paternal allele is 11, which the alleged father carries

A child receives one allele from each parent. The mother cannot have given allele 11, so allele 11 must come from the biological father. The alleged father carries 11, so he is consistent at this locus. Many loci are compared before a probability of paternity is stated.

Option by option

A. The obligate paternal allele is 10, which the alleged father lacks
Allele 10 is carried only by the mother and is not seen in the child.
B. The obligate paternal allele is 9, which the alleged father lacks
Allele 9 is present in the mother and could be maternal, so it is not the obligate paternal allele.
C. The obligate paternal allele is 13, which the child lacks
Allele 13 is not present in the child, so it cannot be the transmitted paternal allele.
D. The obligate paternal allele is 11, which the alleged father carries (correct)
Correct. The mother cannot supply 11, so 11 is the obligate paternal allele and he carries it.

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 obligate paternal allele is 11, which the alleged father carries. A child receives one allele from each parent.

Why is "The obligate paternal allele is 10, which the alleged father lacks" not the answer?

Allele 10 is carried only by the mother and is not seen in the child.

Why is "The obligate paternal allele is 9, which the alleged father lacks" not the answer?

Allele 9 is present in the mother and could be maternal, so it is not the obligate paternal allele.

Why is "The obligate paternal allele is 13, which the child lacks" not the answer?

Allele 13 is not present in the child, so it cannot be the transmitted paternal allele.

What concept does this question test?

It tests Identification: STR profile in paternity testing in Forensic Medicine. The mother cannot have given allele 11, so allele 11 must come from the biological father. The alleged father carries 11, so he is consistent at this locus. Many loci are compared before a probability of paternity is stated.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: STR profile in paternity testing?

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.