Body tissues affect twins' genes
Every mother of identical twins knows how to tell her children apart.
Now scientists have found evidence of effects before birth that could account for some of the differences.
On paper, identical twins that share the same womb and set of genes should be indistinguishable.
But the activity of their genes can be affected by environmental factors unique to each of them.
Researchers identified widespread differences of this kind in the genes of identical twins at birth.
They believe they can be traced to the influence of tissues such as the placenta and umbilical cord that are specific to each twin.
Genes are affected by environmental factors through a chemical process called epigenetic tagging, which acts like a switch turning them on or off.
In the new study, scientists looked at the epigenetic profiles of umbilical cord and placenta tissue, and cord blood from pairs of newborn identical and non-identical twins. Even in identical twins, they were significantly different.
"This must be due to events that happened to one twin and not the other," said lead researcher Dr Jeffrey Craig, of the Murdoch Children's Research Institute (MCRI) in Australia.
The study is reported online in the journal Genome Research.