What Is Down Syndrome?

The National Down Syndrome Society is an excellent resource in learning more about Down syndrome:

In every cell in the human body there is a nucleus, where genetic material is stored in genes.  Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes.  Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm - although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.  Continue reading.

Karyotype of a male with Trisomy 21