“Differences between Germline Genomes of Monozygotic Twins”, Hakon Jonsson, Erna Magnusdottir, Hannes P. Eggertsson, Olafur A. Stefansson, Gudny A. Arnadottir, Ogmundur Eiriksson, Florian Zink, Einar A. Helgason, Ingileif Jonsdottir, Arnaldur Gylfason, Adalbjorg Jonasdottir, Aslaug Jonasdottir, Doruk Beyter, Thora Steingrimsdottir, Gudmundur L. Norddahl, Olafur Th. Magnusson, Gisli Masson, Bjarni V. Halldorsson, Unnur Thorsteinsdottir, Agnar Helgason, Patrick Sulem, Daniel F. Gudbjartsson, Kari Stefansson2021-01-07 (heritability; similar)⁠:

Despite the important role that monozygotic twins have played in genetics research, little is known about their genomic differences.

Here we show that monozygotic twins differ on average by 5.2 early developmental mutations and that ~15% of monozygotic twins have a substantial number of these early developmental mutations specific to one of them. Using the parents and offspring of twins, we identified pre-twinning mutations. We observed instances where a twin was formed from a single cell lineage in the pre-twinning cell mass and instances where a twin was formed from several cell lineages.

CpG>TpG mutations increased in frequency with embryonic development, coinciding with an increase in DNA methylation. Our results indicate that allocations of cells during development shapes genomic differences between monozygotic twins.

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