Rare Semi-Identical Twins Discovered

[rodeodance]

ho ho, another cateogory to remember!


http://news.yahoo.com/s/livescience/20070326/sc_livescience/raresemiidenticaltwinsdiscovered;_ylt=AtAs6S.wgneH5arK3mVYRUxxieAA

Rare Semi-Identical Twins Discovered

LiveScience Staff

LiveScience.com Mon Mar 26, 10:01 AM ET

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.

Here's how it happened: Two sperm cells fertilized one egg—an event assumed to be very rare—then split into two embryos.

"Their similarity is somewhere between identical and fraternal twins," said geneticist Vivienne Souter, of the Banner Good Samaritan Medical Center in Phoenix, Arizona. "It makes me wonder whether the current classification of twins is an oversimplification."

[dflprincess]

1. I watched a fascinating show on Discovery about multiples a while back

though in that case they thought the semi-identical twins are the result of the egg splitting before it's fertilized and then fertilized by two different sperms.

The other interesting thing was, that scientists don't like the term "identical", they prefer monozygotic. One reason for this being that, if a fertilized egg has a XXY sex chromosome configuration, it can split and somehow or another one of the twins winds up being XX (female) and the other is XY (male) - so it's possible to have monozygotic twins who are different sexes.