Question

trisomy 21 (down syndrome) is a result of which of the following? nondisjunction, crossing over, mitosis, transcription

Explanation:

Trisomy 21 (Down Syndrome) occurs when an individual has three copies of chromosome 21 instead of the typical two. This extra chromosome arises from a failure of chromosome pairs to separate properly during cell division, a process called nondisjunction. Crossing over is a normal genetic recombination event, mitosis is regular body cell division, and transcription is the process of making RNA from DNA, none of which cause trisomy 21.

Answer:

A. Nondisjunction