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Consider a gamete in a typical human being. In the interest of being specific, let us say that we're talking about a typical ovum in a typical middle class woman living in a developed nation. What percentage, on the average, of the mutations in the genome of that ovum will have been caused by electromagnetic radiation?

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    $\begingroup$ May we also assume the person lives at sea level? The sun will, by far, be the greatest source of radiation in an average person's life (in practically any location). Elevation is likely to be a key variable in how much radiation she receives (doubles every 6k ft). Radon-222 probably deservers an honorable mention, but no matter what the radiation source, the answer is going to be a very, very low percentage. $\endgroup$ – Atl LED Aug 15 '14 at 1:38
  • $\begingroup$ @AtlLED, yes absolutely, and that is a very good point. $\endgroup$ – goblin Aug 15 '14 at 9:33
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You might use the frequency of thymine-thymine dimers to extrapolate the rate of UV induced damage. This has been studied but I couldn't find a paper in human cell lines. It appears different cell lines have different susceptibilities to thymine-thymine dimers. The majority of DNA mutation in healthy people comes from endogenous sources, not radiation. Recombination during fertilization may also contribute significantly to changes in DNA sequence. Wikipedia nicely breaks down some of the different sources of mutation.

Manifestations of mutations from endogenous sources is measurable as our bodies become genetically more chimeric with time. Regions of our bodies become deferentially susceptible to disease due in largest part to errors in DNA repair and replication, unrelated to electromagnetic insult.

Damage due to UV radiation, like the creation of a thymine-thymine dimer, can be repaired readily by base excision and replacement. While DNA is dividing, it is cut many times to allow the molecule to unwind. Single strand breaks resulting from DNA damage have robust mechanisms for repair. For example, when a thymine-thymine dimer is excised or single strand break is otherwise introduced, enzymatic recognition makes identification of a template for repair possible. It is also very unlikely in a single strand break that another break will occur in the same location, decreasing the mutation effect of UV.

Double strand breaks and errors in DNA replication are intrinsically more permanent as a substituted base is chemically indistinguishable from any other of the same type. Much of the new genetic information introduced into any mammalian genome comes from endogenous sources, not the environment.

  1. Error rate of human DNA polymerase
  2. Deamination is a major contributor to mutation rate
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  • $\begingroup$ The only problem with this, is that the germline should absolutely not be exposed to UV radiation. One of the big things mammals got right was the whole "mama" thing. In fact, the mother not getting enough UV exposure for vitamin production is more likely to be a problem. $\endgroup$ – Atl LED Aug 15 '14 at 13:10
  • $\begingroup$ Good point. Now I want to know the correlation between different products of DNA damage and energy of insulting light. Maybe the success of internal fertilization for animals with small litter sizes is related to protection from UV. $\endgroup$ – 12345678910111213 Aug 15 '14 at 21:13

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