Medical genetics: mosaicism: practice question

The best answer is D, Mitotic nondisjunction after fertilisation in an early embryonic cell. Mosaicism means that cells of one individual have different karyotypes, usually from postzygotic mitotic nondisjunction.

A meiosis II error also gives non-mosaic trisomy because the abnormal gamete affects all cells.

A Robertsonian carrier parent would produce translocation Down syndrome with 46 chromosomes in all cells.

Meiotic error produces a zygote trisomic in every cell and causes full Down syndrome.

It tests Medical genetics: mosaicism in Anatomy. Only the descendants of the abnormal cell line are trisomic, so the phenotype is often milder. Nondisjunction in meiosis would produce a zygote with trisomy in all cells.

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.

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

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.