>>Can you read? Most of the time these are not genetic effects.
From your original Post:
[Typically chimeras originate from two embryos fusing in the womb]
And why does this defect take place?
Could it be because the mother has a defect in the DNA that codes for the enzymes involved in embryonic development?
Or maybe she has a defect in the DNA that recognizes and spontaneously aborts "birth defects".
Perfectly plausible hypothesis.
Quack quack waddle waddle... Oh look, it's genetic.
No. Chimerism occurs when two normal embryos fuse or when cells from one normal embryo are transferred to the twin embryo. This is a normal occurrance--in fact, mothers who have born a baby boy have a handful of XY cells from their baby scattered through their tissues. It is a testimony to the plasticity of stem cells.
There is a vast difference between proposing a hypothesis and jumping to a conclusion. You have nothing (and there is nothing) to support your position that there is a genetic bias towards chimerism, yet you're putting forth some sort of eugenic program in spite of your ignorance. Not very impressive.