Science Questions

How do mutations occur in human beings?

Sun, 29th Jan 2012

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Rashi Rustagi asked:

Hi Naked Scientists

My question is- how do mutations occur in human beings?






Mutations are damage to the DNA of your cells.  DNA is obviously the instructions for your cells, telling them what to do, so damage to DNA in your cells can cause problems.  Most mutations happen because we breathe oxygen.  But don't stop breathing, you'll probably going to be okay!  Breathing oxygen generates molecules called free radicals within ourselves and these are very damaging to DNA.  Most of the mutations that we get are just patched up all the time.  We have very good DNA repair processes in our cells that fix them, but sometimes mistakes creep in.  Most of the time, these aren’t even important because a lot of the cells in your body are destroyed after a while.  The cells in your gut are constantly turning over, also in your skin, and your bone marrow...  So most of the time, mutations are not that important.  Cells get damaged and they just die and you get rid of them. 

What happens when it becomes really important is when you get mutations in cells that do hang around and in stem cells particularly that can cause problems.  But there are lots of other ways that you can mutate the DNA in your cells.  For example, the carcinogens, the cancer causing chemicals and things like tobacco smoke.  Some things in our environment, some things like benzenes, some air pollution, all sorts of things can damage your DNA.  Another big cause is the Sun.  The ultraviolet light from the Sun causes a very specific type of DNA mutation.  It causes the Thymine bases (the ‘T’s’) that are nearby to fuse together in your DNA.

So there's an awful lot of things that can cause mutations.  Sometimes they don't matter, sometimes they do.  Some of which we can't prevent and a lot of which, our body just repairs naturally.  But the trouble is, when we don't repair them or we keep piling more mutations, or if we have problems with the repair systems in our cells, then you can get problems like cancer and other diseases.


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DNA Reproduction is not exact. 
The cells have error correction routines to improve the accuracy, but end up with an error rate of 1 transcription error in 10-9 to 10-11 nucleotides.

The human genome has about 2.9 x 109 nucleotides.

So, there is somewhere between a couple of uncorrected errors per cell division to an error in every few hundred cell divisions.

The errors can either occur in the gametes, leading to a new mutation that can be passed on, or occur in the normal cell division in the human body, sometimes leading to developmental problems, or to cancers.

Some of the DNA errors are insignificant.  Others may be be be damaging, but since cells are diploid, they may not cause a problem. 

If a baby's mother and father each have a few hundred "mutated" genes, both new mutations, and those from previous generations, then the baby will inherit an imperfect set of genes. 

If the parents unrelated, the likelihood that these mutated genes will be the same would be relatively rare, and the infant will receive one good copy of every gene.  However, if the parents are closely related, then there is a much greater possibility of sharing the same mutations, and getting two mutated copies of genes. CliffordK, Sun, 29th Jan 2012

DNA "switches" that control the DNA  & are 80% of the DNA...PBS CZARCAR, Mon, 30th Jan 2012

Yes copying errors are the main source of mutations in DNA and many are neither advantageous (in an evolutionary sense) or detrimental, there are also mutations causesd by environmental influences such as exposure to certain types of radiation. This can cause direct damage to DNA, resulting in mutations (the poor fruitfly has been at the brunt of research into this). Sadly these mutations are usually relatively mundane in their expression: no bone claws or healing factor… Devilmunkey, Mon, 13th Feb 2012

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