Trisomy 21, commonly known as Down's Syndrome, is a chromosomal disorder characterized by the presence of an extra copy of chromosome 21 in the human genome. Normally, humans have 46 chromosomes arranged in 23 pairs, but in Trisomy 21, there are three copies of chromosome 21 instead of the usual two. This additional genetic material disrupts normal development and leads to a combination of physical, cognitive, and medical features. The primary cause of Trisomy 21 is nondisjunction during meiosis, where chromosome 21 fails to separate properly, resulting in gametes with an abnormal number of chromosomes. Less commonly, Down's Syndrome may result from translocation or mosaicism, where only a portion of the body’s cells carries the extra chromosome. Individuals with Down's Syndrome typically exhibit characteristic facial features such as a flat facial profile, upward-slanting eyes, small ears, and a protruding tongue. Other features include hypotonia (low muscle tone), short stature, single palmar crease, and developmental delays. Cognitive impairment varies widely but generally ranges from mild to moderate intellectual disability. Down’s Syndrome is also associated with medical complications such as congenital heart defects,