The researchers used in-bred mice strains to essentially do the experiment suggested by James Boettcher. Some epigenetic marks are made during development in the womb, but many are already established in egg and sperm that lead to the fertilized embryo.
The researchers speculate that early splitting twins are more similar because the split occurs before differentiation of cells toward specific cell types. Early-splitting embryos therefore contain the same basic epigenetic program. In later-splitting embryos, one twin would carry epigenetic marks established as the cells it originated from began to differentiate. Those marks would be absent in the other twin and vice versa, leading to greater epigenetic diversity in the late-splitting twins.

Tuesday, February 24th, 2009 4:55 pm by Tina Hesman Saey

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