Chimerism: I'm confused about where the non-maternal genome comes from. Can somebody explain please?

Question

It recently occurred to me that I missed out on understanding this phenomena called chimerism.

I recall seeing a few specials back in August 2006 about Lydia Fairchild on ABC networks.

I didn't quite understand the big "theme" here, to explain how the kids share no genetic identity with their biological mother.

I have followed up recently on the story, reviewed the story, and it is still not making sense to me.

Does anyone have a website to share, which might show the pedigree for this phenomena?

Or, would anyone be willing to explain to me how Lydia Fairchild's haploid genome was swapped with someone else's genome?

The concept of "you are your own twin" would be made clear after testing both parents of Lydia, right? Or did I miss in the story that one parent (or both) were not available for genetic testing.

Thanks for your help!

Here is a link, in case you forgot the details regarding this story.

http://abcnews.go.com/Primetime/story?id=2315693&page=1

Answer 1

Chimeras are formed from four parent cells (two fertilized eggs or early embryos are fused together) or three parent cells (a fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm). Each population of cells keeps its own character and the resulting animal is a mosaic of mis-matched parts. An analogy is two jigsaw puzzles cut using an identical cutter, but with different pictures. A single puzzle can be made out of the mis-matched parts, but the completed puzzle will show parts of both different pictures. The likelihood of a child being a chimera is increased if the child is created via in vitro fertilization. Chimeras can often breed, but the fertility and type of offspring depends on which cell line gave rise to the ovaries or testes.