Trisomy is a condition in which a person's cells
have three chromosomes in a single set. Normally, a person's chromosomes come
in pairs and humans have 23 pairs of these chromosomes (46 in total).
When a person has a trisomy disorder, an additional chromosome is found in one
of the pairs of chromosomes. When this happens the individual has a total of 47
chromosomes in his cells. Down syndrome, Edward syndrome, and Patau syndrome
are the most common gene abnormalities caused by trisomy disorder.
