Please see other e-mail, marked "part 1", for first half of article.
Jaro
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MCDONALD: Well, how did you go about looking at the impact this radiation might have genetically on this population?
FORSTER: Well, what we look at for different purposes... we actually do evolutionary research. We look at a part of our DNA which is handed down entirely through the maternal lineage, through the mothers. And this is called mitochondrial DNA, or MT DNA for short. And we looked at this DNA because it's very easy to trace within families. You always know yours comes from your mother, your mother's from her mother, and so on. There's no difficulty in finding out where a type comes from. So if we see a mutation happen we simply have to trace the maternal lineage to find out its effects. For example, my wife would have sampled, say, a grandmother then her daughters and then the granddaughters. And all we'd have to do in the laboratory is to determine the grandmother's sequence and one of the granddaughters', and if we see a difference between the two we can then go and take a look at the inter... intervening generation to see where that mutation happened and how it was passed down to other daughters or whether it was passed down at all. So this is a very simple genetic system which is very powerful for... for finding mutations in families.
MCDONALD: So you're looking for mutations that have happened over time, in other words, that have been passed down through the generations.
FORSTER: Exactly.
MCDONALD: So what did you see when you looked at the mitochondrial DNA of these families that have been living in this high-radiation area?
FORSTER: When we compared the radioactive area with the non-radioactive area next door... we were comparing about 750 individuals from the radioactive area and 250 from the non-radioactive control area... we saw they had significantly more mutations in the radioactive area, so 22 mutations in the radioactive area and only one mutation in the non-radioactive area.
MCDONALD: So how meaningful is that? What does that mean that they have these mutations?
FORSTER: Well, it is... first of all, you might be interested in the health effects. Now, because we looked at a region of our genome which does not code for a gene, so it does not create any visible effects, whether beneficial or adverse, but there's no reason to suppose that mutations here of course are restricted to such non-coding regions. We have to assume that other genes, like for example, cancer genes, will be equally affected by these mutations. Now, the other interesting finding we had was that the mutations which have occurred in these families within the last two or three generations we looked at are the same mutations at the same DNA positions as have mutated in the past 60,000 years of human evolution. And this means radioactivity is triggering or accelerating a general mutation mechanism which is also causing our DNA to evolve.
MCDONALD: Are you saying that the... this higher level of natural radiation is actually accelerating human evolution?
FORSTER: In a sense, yes, because the mutations which occur are at the same positions that have mutated in the past 60,000 years. We can tell which positions have mutated if we look at all humans and then reconstruct their evolutionary tree for this particular molecule. And then we see that some positions have mutated very frequently and others haven't mutated at all. And when we now look in the radioactive families we see exactly the same pattern. The ones that are known to be so-called mutational hot spots are also hot spots which mutate frequently in our radioactive families.
MCDONALD: But did we know that these mutations that have been happening to us throughout our evolution were caused by natural radiation?
FORSTER: That is a hot potato. I... I know that there are some geneticists who believe that most of the changes that have happened during evolution are due to defects in our repair mechanism. And another idea is that there might be chemical forces at work actively modifying DNA through chemical contaminants or ultraviolet radiation and the like. I certainly think that radioactivity has something to do with the mechanism, and it might explain a lot of what we see during evolution.
MCDONALD: Were you surprised that you saw these mutations at... at such low levels?
FORSTER: In fact, I was. If we look at the level of radiation in normal areas it's about one millisievert. This is what most humans across the world receive. In Kerala it's ten millisieverts. It's ten times as much. If we look at the level allowed for people working with radiation professionally, they are allowed a maximum of 50 milliseverts. And if we see effects at ten milliseverts, then I think we should be careful with a level of 50 milliseverts as a legal maximum.
MCDONALD: What are you suggesting the legal maximum should be?
FORSTER: Well, that'll depend on more research, but I think if even a tenfold increase does cause such observable changes, we should be considering a level which is perhaps at most that.
MCDONALD: Dr. Forster, thank you very much for your time.
FORSTER: My pleasure. Thanks.
MCDONALD: Dr. Peter Forster is a research fellow in the Molecular Genetics Laboratory at the McDonald Institute at the University of Cambridge.
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