Scientists have been fascinated with Identical Twins DNA since the genome code was exposed in 1952. Since the 1980s it has been believed that Identical Twins were a perfect match, not only in looks and dispositions, but in their DNA.

Though it is almost perfectly identical, the twins DNA do have a small difference. In 2005, at the University of Alabama Department of Genetics, researchers did tests on Identical Twins and found a difference in their Copy Number Variation (CNV).

Copy Number Variation (CNV) is a segment of DNA in which differences have been found by comparison of two or more genomes (a full set of chromosomes). For example, one twin might be missing a segment, or possess more copies of that segment than the other twin.

This would explain why one twin could have a disorder the other doesn't have. It also goes to show that even when things appear to be identical, you can always find a difference.

The DNA of Identical Twins is "magic DNA" in the science world. When one twin is sick and the other is not, you can analyze their DNA to observe their differences.

Identical Twins DNA Test at Ancestry.com DNA testing