Which genetic abnormality is associated with the presence of an extra chromosome 21?

Down Syndrome, also known as Trisomy 21, is specifically associated with the presence of an extra copy of chromosome 21. This genetic anomaly leads to a range of developmental and physical differences that are characteristic of the condition. Individuals with Down Syndrome often exhibit distinct facial features, potential cognitive delays, and an increased risk for certain medical conditions.

Turner Syndrome involves a missing or partially missing X chromosome in females, Klinefelter Syndrome involves an extra X chromosome in males, and Edward Syndrome, known as Trisomy 18, is due to the presence of an extra chromosome 18. Each of these conditions displays its own unique chromosomal abnormalities and clinical features distinct from those seen in Down Syndrome.