Down syndrome is caused by which of the following genetic anomalies?

Down syndrome is primarily caused by a genetic anomaly known as trisomy 21, which is the triplication of chromosome 21. In individuals with Down syndrome, there are three copies of this chromosome instead of the usual two. This additional genetic material alters the course of development and causes the characteristic features and health challenges associated with the condition.

Understanding the nature of this genetic alteration is key; it leads to the typical physical traits and cognitive challenges that people with Down syndrome experience. The presence of an extra copy of chromosome 21 can result from several factors, including errors during cell division in the formation of eggs or sperm, where a failure in proper chromosome separation occurs.

Other options would involve different genetic mechanisms that do not cause Down syndrome, such as deletions, mutations, or translocations involving other chromosomes. These do not relate to the specific chromosomal abnormality associated with Down syndrome. Therefore, the triplication of chromosome 21 is the defining genetic cause of this condition.