What genetic condition results from three chromosomes on pair 21?

Down Syndrome, also known as Trisomy 21, occurs when an individual has three copies of chromosome 21 instead of the usual two. This genetic anomaly is responsible for a range of developmental delays and physical characteristics associated with the condition. Individuals with Down Syndrome often exhibit distinct facial features, cognitive impairments, and an increased risk for certain health issues.

The additional copy of chromosome 21 leads to an overexpression of the genes located on this chromosome, which contributes to the symptoms and characteristics associated with Down Syndrome. Recognizing this genetic basis is crucial for understanding its implications in physical and intellectual development, as well as for providing appropriate support and interventions for affected individuals and their families.

The other conditions listed are caused by different genetic factors or environmental influences and do not involve the presence of an extra chromosome on pair 21.