Science Questions

Do we have areas of our bodies with different genes owing to mutation?

Mon, 5th Sep 2016

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Angelo Odato asked:

Our cells are dividing all the time ... billions of times. There must be many mutations during these divisions and some of these get propagated. Do we have areas of our bodies with different genetics?



Angelo Odato





Kat fills us in on this question about genetic mutations...Dnahelix_genetic_fingerprint

Kat - This is a fantastic question because the answer is kind of yes. We will pick up mistakes, changes, mutations whether thatís from the processes of life like copying DNA or from the oxygen that weíre using to make energy that damages DNA loads and loads, and loads. Also, there are chemicals in the environment and things like ultraviolet light, chemicals in tobacco smoke that can damage the DNA in different cells and that can be propagated if those cells divide. So yeah, we are made up of probably a little bigger or smaller clumps of cells that are all very, very slightly different. Obviously, a good example of where this really goes wrong is cancer because thatís when cells have picked up a number of mistakes that have made them start growing out of control.



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Slightly. Occasionally the mutation gets really out of hand and that's (at least) one route to cancer. Bored chemist, Tue, 19th Jul 2016

Yes. Out of the billions of DNA "letters" in each of our cells, it is common to find one or more random copying errors each time a cell divides.

It is unlikely that a copying error will occur in exactly the same place when a different cell divides, so it is possible that every cell in your body has a unique DNA sequence. But they are still 99.9999% identical.

Fortunately, our cells have a built-in mechanism that limits the build-up of mutations - most human cells will only divide around 40-60 times before they stop dividing - the Hayflick Limit. But that also means that we get old!

A more extreme form of different DNA is microchimerism, where cells from a baby may live on in the mother's body (or vice-versa). 

Even more extreme is chimerism, where two fertilized egg cells may merge, producing an individual who has different organs with different DNA. This has produced some weird results when DNA tests are run, like "your child is actually your nephew". evan_au, Tue, 19th Jul 2016

As I understand it, microchimerism isn't unusual - most mothers have some of their babies cells still hanging around. dlorde, Tue, 19th Jul 2016

This is a very nice article about microchimerism by Dalya Rosner; one of the first guest articles we published on the Naked Scientists, but still extremely readable... chris, Tue, 19th Jul 2016

Another source of genetic variation in our bodies is due to mutations, which can come from the products of cell metabolism, natural radioactivity, chemicals in the environment, viruses and exposure to ultraviolet light from the Sun.

Most of these mutations are repaired by the cell, but not always identically to the original.

It is estimated that a typical cell could suffer between 10,000 and 1,000,000 mutations per day.
Each cell will accumulate a unique set of mutations over its lifetime, and will pass them on to its daughter cells when it divides.

evan_au, Wed, 20th Jul 2016

Another part of our bodies that have a unique genetic identity is egg cells and sperm cells, which have half of the normal number of chromosomes.

Due to the way these reproductive cells are formed, each cell has a unique set of genes. evan_au, Wed, 20th Jul 2016

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