Tuesday, October 18, 2016

How does genetics explain non-identical identical twins?

Colin Moran

Newspapers recently went wild with a story about identical twin sisters with a difference: they weren’t identical. Like all identical twins, Amelia and Jasmine arose from a single fertilised egg so have identical DNA, but somehow look different from each other.   One child has dark skin, black hair and brown eyes while the other has fair skin, light-brown hair and blue eyes.

How is this possible?   Have the doctors or scientists got it wrong? No one has got it wrong. They really are identical twins.

While this is a rare event – the doctors were as surprised as anyone – genetic and epigenetic research tells us that it is possible. In fact, it is likely to be the result of common biological processes that are going on inside all of us all of the time – although, typically, with less visually striking effects.........

Consequently, identical twins do not actually share 100% of their DNA although they share very close to 100%. And when the differences are in the genes responsible for features such as hair colour, eye colour or skin colour, twins will have obvious and dramatically different looks......

In addition to this, genes can be switched on and off in different cells. In fact, they have to be. If all of our genes were switched on all of the time in all of our cells then we would not be able to grow different tissue types and organs from a single set of biological instructions. .......To Read More...

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