"Twins can be identical, fraternal and apparently semi-identical, scientists now report. Researchers discovered twins who are identical on their mom's side of the equation but share only half their genes from dad." Link: http://news.yahoo.com/s/livescience...sdiscovered;_ylt=AovilSsdvmHjaJ8OoxqkX3gDW7oF Very interesting. I had identical twins as roommates in college. Their parents were also identical twins. Their parents' twins also married each other.