Which of the following describes Down syndrome?

Down syndrome is primarily characterized by the presence of an extra chromosome 21, which is referred to as trisomy 21. This genetic disorder arises when there is an error in cell division during the formation of the reproductive cells, leading to an individual having three copies of chromosome 21 instead of the usual two. This chromosomal abnormality results in the physical and cognitive characteristics associated with Down syndrome.

The focus on genetic principles is crucial in understanding Down syndrome, as it emphasizes that this condition is not due to infections, environmental influences, or parental genetic contributions alone. It is specifically the result of this chromosomal anomaly that differentiates Down syndrome from other conditions that might be influenced by such factors. This comprehensive understanding helps clarify the nature of the disorder as inherently genetic and highlights its distinct mechanism of formation.