Identification: ABO grouping in disputed paternity: 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: ABO grouping in disputed paternity

Sample item

In a disputed paternity case the mother is group A and her child is group O. The alleged father is group AB. What can be concluded from the ABO grouping?

AHe is excluded, since a group AB man cannot transmit an O alleleBHe is not excluded, since an AB man can transmit either A or B to a group O childCHe is not excluded, since the mother is group ADThe grouping cannot be interpreted without Rh typing

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

The answer and the reasoning

A. He is excluded, since a group AB man cannot transmit an O allele

A group O child is homozygous for the O allele and must receive one O allele from each parent. A group AB man has only A and B alleles and cannot give an O allele, so he is excluded. Blood grouping can only exclude paternity and cannot prove it.

Option by option

A. He is excluded, since a group AB man cannot transmit an O allele (correct)
Correct. An AB man has no O allele to pass to a group O child.
B. He is not excluded, since an AB man can transmit either A or B to a group O child
A or B alleles would give a child of group A, B or AB, never group O.
C. He is not excluded, since the mother is group A
The mother being group A does not matter, because the father still has to supply an O allele.
D. The grouping cannot be interpreted without Rh typing
Rh typing is independent of the ABO system and does not change this exclusion.

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 A, He is excluded, since a group AB man cannot transmit an O allele. A group O child is homozygous for the O allele and must receive one O allele from each parent.

Why is "He is not excluded, since an AB man can transmit either A or B to a g…" not the answer?

A or B alleles would give a child of group A, B or AB, never group O.

Why is "He is not excluded, since the mother is group A" not the answer?

The mother being group A does not matter, because the father still has to supply an O allele.

Why is "The grouping cannot be interpreted without Rh typing" not the answer?

Rh typing is independent of the ABO system and does not change this exclusion.

What concept does this question test?

It tests Identification: ABO grouping in disputed paternity in Forensic Medicine. A group AB man has only A and B alleles and cannot give an O allele, so he is excluded. Blood grouping can only exclude paternity and cannot prove it.

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: ABO grouping in disputed paternity?

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.