Beginning of Essay
In one in every one thousand births, an extra chromosome results in the birth of a baby with Down's Syndrome; a genetic disorder resulting in mental retardation. In 1866, physician John Langdon Down, in Surrey England, identified a set of children with common fe ....

Middle of Essay
.... the mutation of autosomal cells which results in three major types of Down's syndrome. Trisomy 21, involves the presence of extra genetic material on the twenty first pair resulting from an anomaly in cell division during the development of egg or sperm during fertilization. About 95% of Down's syndrome births are Type Trisomy 21. Roughly 4% are caused by Translocation, "where the extra chromosome twenty one is broken off and becomes attached to another chromosome pair. The last 1% have Mosaicism, where only some cells of the chromosome have extra genetic material. With the different types of Down's the degree of retardation ranges from mild to sever. ....