Identical twins aren't always genetically identical, new study finds

Twin studies have long been used to examine the effects of nature versus nurture.

(CNN)Identical twins may not be quite as identical as we thought; researchers in Iceland have discovered genetic differences that begin at the early stages of embryonic development.

Scientists have long used the study of identical twins to examine the effects of nature versus nurture, as the accepted view has been that, because they share the same genes, any physical or behavioral differences between such siblings must be down to outside influences.
However, this may not be the case, suggested the new research, published Thursday in the journal Nature Genetics.
Identical twins come from a single fertilized egg, or zygote.
In any embryo, cell division can lead to mutations, but this type of genetic difference had not previously been measured between identical twins.
Over the course of a four-year study, a team of Icelandic researchers at DeCode Genetics, a Reykjavík biopharmaceutical company, found that monozygotic, or identical, twins have genetic differences that begin in the early stages of embryonic development
The scientists sequenced the genomes of 387 pairs of identical twins and their parents, spouses and children to track mutation divergence. The authors foun