The 21번 염색체 is one of the 23 pairs of chromosomes found in humans. It is the smallest human chromosome and contains about 48 million base pairs. This chromosome plays a crucial role in various genetic functions and is involved in the development of certain traits. Abnormalities in the 21번 염색체 can lead to genetic disorders, the most well-known being 다운 증후군 (Down syndrome). This condition occurs when there is an extra copy of the 21번 염색체, resulting in three copies instead of the usual two. This genetic variation can affect physical and cognitive development.