So if there's two dads, are the twins still identical?

[LiberalHeart]

An odd story (at least to me, because I'd never heard of this "polar twins" thing before):

http://newsgrinder.blogspot.com/2007/03/semi-identical-twins-dna-matches-on.html

[hobbit709]

1. Same dad

2 different sperm cells

[LiberalHeart]

5. I don't understand ... how can it be one guy, not two?

Would the dad's genetic markers change on a per-sperm basis? (Do I need to take biology 101?)

[merwin]

2. That's a trip...

[uppityperson]

3. semi-identical=no. Here is another article, it is very odd. Thanks for the info about this.

http://www.livescience.com/humanbiology/070326_semi_twins.html
(clip) "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."
(clip)
Identical twins are created when one fertilized egg splits into two embryos. They share the same placenta and are always of the same sex. Fraternal twins result from two eggs being fertilized at the same time, each by a different sperm. Each has its own placenta, and they can be the same sex or not.

The semi-identical twins only came to the attention of Souter and her colleagues because one had ambiguous genitalia. The child was born a "true hermaphrodite" with both ovarian and testicular tissue. The other twin is a male, anatomically.

[Bunny]

4. Both sperm came from the same dad.

But I didn't think this was possible - I thought that only one sperm got into the egg, and if somehow a second one made it in, the embryo would be incompatible with life.