How Identical are Identical Twins? | Read Through Transcription

How Identical are Identical Twins?
December 19, 2011 by Ramesh Hariharan
We're looking at exome sequencing data on whole peripheral blood DNA of monozygotic twins (this data was generated by our collaborators, Jan Dumanski and his group at Uppsala University in Sweden). Monozygotic twins were earlier thought to be genetically identical; now we know that isn't completely true. How does one identify small mutations (SNPs and small InDels)  that are present in one of the twins but not in the other? Or in general, how does one compare two different samples, for instance, to find somatic mutations that are present in a tumor sample but not present in the paired normal sample.
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The 1000 Genomes Project estimated that a child has only around 50 new mutations relative to its parents. Monozygotic twins ought to be closer than that. And we are observing only the exomes (and some neighborhood) of these twins. So the real answer probably lies close to the bottom of the above table. However, as Jan Dumanski points out, much of the 1000 Genomes effort involved sequencing of oligoclonal/monoclonal lymphoblastoid cell lines, not quite directly comparable with whole peripheral blood.

http://blog.avadis-ngs.com/2011/12/how-identical-are-identical-twins/

gosh who knew calling SNPs on identical twins can be a complicated task??


update:
related links I found
Different sides of the same coin; twins and epigenetics

http://blogs.dnalc.org/2011/09/23/different-sides-of-the-same-coin-twins-and-epigenetics/