Identical twins aren’t perfect clones


Scientists in Iceland sequenced DNA from 387 pairs of identical twins – those derived from a single fertilized egg – as well as from their parents, children and spouses. That allowed them to find “early mutations that separate identical twins”.


Genetic mutations

  • A mutation means an alteration in a sequence of DNA – a tiny change that is not inherently good or bad, but can influence physical features or susceptibility to certain diseases. 
  • They can occur when a cell divides and makes a slight error in replicating DNA.


Identical twins

  • On average, identical twins have 5.2 of these early genetic differences, the researchers found. 
  • But about 15% of identical twin pairs have more genetic differences, some of them up to 100.
  • These differences represent a tiny portion of each twin's genetic code, but they could influence why one twin is taller or why one twin is at greater risk for certain cancers.
  • Previously, many researchers believed that physical differences between identical twins were related mostly to environmental factors, such as nutrition or lifestyle.
  • The implication is that we have to be very careful when we are using twins as a model, for teasing apart the influences of nature and nurture.
  • The new study goes beyond earlier work by including DNA of parents, children and spouses of identical twins
  • That allowed the researchers to pinpoint when genetic mutations occurred in two different kinds of cells – those present in just one individual and those inherited by that person’s children
  • They also found mutations that occurred before the developing embryo split into two, setting the stage for twins.
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