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Identical Genes, Individual Twins

Photo: Fotostudio Enjoy, Ingrid van Heteren (NL)

Identical twins essentially have the same DNA sequence, but the way they use their DNA can be vastly different. Photo: Fotostudio Enjoy, Ingrid van Heteren (NL)

By Marcel Coolen

Identical twins essentially have the same DNA sequence, but the way they use their DNA can be vastly different. Photo: Fotostudio Enjoy, Ingrid van Heteren (NL)

The research described here was performed by Dr Marcel Coolen at the Garvan Institute of Medical Research’s Epigenetics group headed by Professor Susan Clark. Dr Coolen is currently group leader at the Department of Human Genetics, Radboud University Nijmegen Medical Centre, The Netherlands.

The full text of this article can be purchased from Informit.

About once every 80 live births, a twin pair is born. The majority of these twins are fraternal, meaning they are derived from two separate fertilisations and are as similar genetically as brothers or sisters.

It is only once in every 250 deliveries that a single embryo splits after fertilisation. This event results in the formation of “identical” twins. As these twins are derived from the same fertilisation, they have identical genomes. Yet, somehow identical twins become increasingly different over time, with subtle differences in their personalities, how they look, how they act and even in their susceptibility to getting a certain disease, such as autism spectrum disorders, schizophrenia, bipolar disorder, epilepsy and diabetes.

The cause of this has to do with their “epigenome”, or how differently they use their DNA. But let’s start with some background.

The genetic sequence of an individual is more or less static over time. Still, the genome has the remarkable ability to dynamically respond to its environment. This is because DNA is only half the story.

Every living cell contains about 2 metres of DNA. To fit this DNA neatly into the tiny nucleus, it is wrapped around proteins called histones. Both these histones and the DNA itself can harbour chemical modifications that can activate or repress the underlying DNA sequence.

This...

The full text of this article can be purchased from Informit.