[Karen W. (OP)]

I have been waching a show where a couple women have given birth to children who do not have her own dna but carry the dna of their mothers family... how oes that happen? I have forgotten  what they call people who are like this..

they say its rare and their are something  like 40 or so known cases...Anyone know any more about it?

[RD]

You may be referring to Chimerism...

Chimerism can be detected in DNA testing. The Lydia Fairchild case, for example, was brought to court after DNA testing showed that her children could not be hers, since DNA did not match. The charge against her was dismissed when it became clear that Lydia was a chimera, with the matching DNA being found in her cervical tissue. Another case was that of Karen Keegan.

http://en.wikipedia.org/wiki/Chimera_%28genetics%29

Human chimeras sometimes have skin markings called "Blaschko’s lines" ...
http://www.thetech.org/genetics/ask.php?id=75