Identical Twins Accumulate Genetic Differences in the Womb

DNA replication errors during cell division cause monozygotic twins to diverge from each other even during the earliest stages of development, a new study finds.

Written byCatherine Offord

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Identical twins are not as identical as previously assumed, according to a study published today (January 7) in Nature Genetics. Rather than having exactly the same DNA sequences, twins start accumulating genetic variation from the earliest stages of development, researchers at Iceland-based company deCODE genetics found, meaning that one twin harbors variants that aren’t present in the other.

Also known as monozygotic twins because they develop from a single fertilized egg, identical twins have long been central to research on the relative effects of genes and environment—aka “nature versus nurture.” Although everyone accumulates some genetic mutations during their lifetime, the differences in identical twins were assumed to be minimal, particularly when twins are young, allowing researchers to study how different environments influence the development of people with the same genotype.

The new study focuses specifically on mutations that occur as or before embryos form from the mass ...

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Meet the Author

Catherine Offord
After undergraduate research with spiders at the University of Oxford and graduate research with ants at Princeton University, Catherine left arthropods and academia to become a science journalist. She has worked in various guises at The Scientist since 2016. As Senior Editor, she wrote articles for the online and print publications, and edited the magazine’s Notebook, Careers, and Bio Business sections. She reports on subjects ranging from cellular and molecular biology to research misconduct and science policy. Find more of her work at her website.
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