Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: thedoc on 19/07/2016 12:50:02
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Angelo Odato asked the Naked Scientists:
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?
Thanks,
Angelo Odato
What do you think?
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Slightly. Occasionally the mutation gets really out of hand and that's (at least) one route to cancer.
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Do we have areas of our bodies with different genetics?
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 (https://en.wikipedia.org/wiki/Hayflick_limit). But that also means that we get old!
A more extreme form of different DNA is microchimerism (https://en.wikipedia.org/wiki/Microchimerism), where cells from a baby may live on in the mother's body (or vice-versa).
Even more extreme is chimerism (https://en.wikipedia.org/wiki/Chimera_(genetics)#Humans), 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".
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A more extreme form of different DNA is microchimerism (https://en.wikipedia.org/wiki/Microchimerism), where cells from a baby may live on in the mother's body (or vice-versa).
Even more extreme is chimerism (https://en.wikipedia.org/wiki/Chimera_(genetics)#Humans), 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".
As I understand it, microchimerism isn't unusual - most mothers have some of their babies cells still hanging around.
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This is a very nice article about microchimerism (http://www.thenakedscientists.com/HTML/articles/article/dalyacolumn7.htm/) by Dalya Rosner; one of the first guest articles we published on the Naked Scientists, but still extremely readable...
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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.
See: https://en.wikipedia.org/wiki/DNA_repair
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Do we have areas of our bodies with different genetics?
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.