Molecular biology and genetics: balanced translocation carriers: practice question

A Biochemistry 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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Biochemistry · Molecular biology and genetics: balanced translocation carriers

Sample item

A couple has had three first-trimester miscarriages. Both partners are phenotypically normal, and karyotyping shows that the woman carries a balanced reciprocal translocation. Why do her pregnancies often fail?

AShe makes antibodies against the translocated chromosomeBHer somatic cells have an extra chromosomeCMeiotic segregation gives gametes with unbalanced chromosome complementsDThe translocation deletes an essential gene in every cell

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

The answer and the reasoning

C. Meiotic segregation gives gametes with unbalanced chromosome complements

In a balanced carrier no genetic material is lost or gained, so she is normal. At meiosis the rearranged chromosomes pair as a quadrivalent and segregate, so many gametes carry a partial trisomy and partial monosomy, causing miscarriage or malformed offspring. Karyotyping of both partners is advised in recurrent pregnancy loss.

Option by option

A. She makes antibodies against the translocated chromosome
An autoimmune mechanism is not involved in the loss of unbalanced conceptuses.
B. Her somatic cells have an extra chromosome
Her somatic cells have the normal number of chromosomes, only rearranged.
C. Meiotic segregation gives gametes with unbalanced chromosome complements (correct)
Correct. Segregation of the translocated chromosomes at meiosis gives unbalanced gametes.
D. The translocation deletes an essential gene in every cell
A balanced translocation does not delete genetic material in her own cells, which is why she is healthy.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Meiotic segregation gives gametes with unbalanced chromosome complements. In a balanced carrier no genetic material is lost or gained, so she is normal.

Why is "She makes antibodies against the translocated chromosome" not the answer?

An autoimmune mechanism is not involved in the loss of unbalanced conceptuses.

Why is "Her somatic cells have an extra chromosome" not the answer?

Her somatic cells have the normal number of chromosomes, only rearranged.

Why is "The translocation deletes an essential gene in every cell" not the answer?

A balanced translocation does not delete genetic material in her own cells, which is why she is healthy.

What concept does this question test?

It tests Molecular biology and genetics: balanced translocation carriers in Biochemistry. At meiosis the rearranged chromosomes pair as a quadrivalent and segregate, so many gametes carry a partial trisomy and partial monosomy, causing miscarriage or malformed offspring. Karyotyping of both partners is advised in recurrent pregnancy loss.

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 Molecular biology and genetics: balanced translocation carriers?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.