Steve Smith wrote in
9.130:

snip

When we found out that we were expecting twins last year, I did a lot
of research. One thing I found was the talk of a third type of twin,
ie not truely fraternal but not truely identical. These supposedly
would come from one egg that splits and gets fertilized with two
sperm. Therefore the mother's half of the genetic material is
identical in both twins, which explains "fraternal" twins that look
remarkably similar. I just googled and found this:
http://www.betterhealth.vic.gov.au/b...pages/Twins_id
entic al_and_fraternal?open

Supposedly this third type of twin is almost impossible to prove and
cannot be distinguished from fraternal (which is just basically
non-identical)



Actually, DNA testing would differentiate between all three possibilities.
Fraternal twins will share 50% of their genes, ID's 99% (I don't think
current tests admit 100% accuracy) and the polar body twins will share
75% of their genetic structure.

Cindy Wells
(who has enough bio and biochem to have heard of many of the issues with
DNA analysis)
Steve