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Comment by bhouston | Hacker News Reader

The human body is incredibly good at detecting unviable mutations during pregnancy and it results in a miscarriage or other failures early on. This would be a much better indicator to look at than whether the children who survived pregnancy had excess mutations.

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That's very true but even if these forces catch 99% of significant mutations then you'd still see an increase in pregnancies resulting from that remaining significant mutations over baseline.

But more importantly, our genomes have a lot of "junk DNA" where a mutation will not affect anything at all and almost everyone has these. From the article it looks like these were the mutations the researchers were looking at.

I remember hearing a hypothesis that "junk DNA" acts as a kind of shielding against mutations. From a probability standpoint, the more non-coding DNA you have, the less likely an error is to hurt the lifeform. Taken to an extreme, if every DNA sequence did something a singe error would cripple the organism.

However, the probability of the DNA getting hit would increase linearly with the amount of junk DNA, wouldn't it? So the chance of good DNA getting hit is exactly the same as without junk.

Not sure how it would help shielding the good DNA, unless it acted as a barrier.

Mutations from radiation come from particles literally slamming into the DNA and screwing it up. The more spaced out the important parts are, the lower the probability that the particle hits a piece of DNA that’s important.

If I place 4 cups of water out in the rain, does their spacing affect how much water lands in each cup?

It depends on how you place them, horizontaly on a table no, in a pyramid yes.

I see what you're getting at, but in this example there would be millions of cups and the individual raindrops would be spread out over a massive area of land.

That doesn’t change anything. The probability an important cup gets hit is always equal to the surface integral of the rain’s flux across the important cup openings. Whether there are unimportant cups nearby doesn’t change anything.

that makes intuitive sense but at least in the case of ionizing radiation it's a little like making a target circle bigger to protect the bullseye which remains the same size. there's still the same chance of hitting the bullseye, no matter how you change the chance of not missing the paper.

Think of it as a 3D sphere instead. You would get a shielding effect.

There is already one milligram of atmosphere over the cross sectional area of a cell nucleus, so it doesn't seem like it could change much for cosmic rays. All DNA in a human cell is about 6 picograms.

That's 166 million times more mass of atmosphere. The elements may be less effective etc. but it still seems like any junk dna shielding would be negligible.

Maybe cosmic rays aren't the main source of ionizing radiation throughout the evolutionary period though.

If the cell around is not shielding it, the little bit of extra DNA is not shielding it either. You need a lot more atoms to get a shielding effect.

I reject the term 'junk dna'. Until we understood the basics of DNA all of it was 'junk', then bit by bit we are making headway into understanding some of it. If we're ever done I predict there will be no junk DNA left. Nature is much too efficient to spend that much energy on something that it ends up not using.

> Nature is much too efficient to spend that much energy on something that it ends up not using.

And yet nature somehow finds it acceptable to grow a nerve all the way from a giraffe's head down its neck, loop around its heart and then go all the way back up through its neck until reaching the head. [0]

[0] https://rationalwiki.org/wiki/Laryngeal_nerve

Yes, and there are a number of other examples like that. But that doesn't detract from the general case in the least: if energy can be saved then it usually will be saved, especially if a mechanism lasts for a long time. The idea that the base mechanism of encoding life patterns is going to be on the order of 70% or more 'junk' requires a very good explanation. Why the argument presented here is invalid I'll leave for you to figure out.

Wouldn’t that depend on the size of the study? Seems like catching an orders of magnitude smaller difference would require orders of magnitude more samples... and the population is only so big..

“Junk DNA” as a concept is pretty dated. It used to refer to non-protein encoding regions of DNA. In our infinite wisdom we assumed these segments of DNA had no purposes yet it turns out they play an important role in DNA packing and unpacking which directly influences gene expression.

Aren't some of these early miscarriages not even known by the woman? Wouldn't that make it difficult to measure?

While that is also a very important indicator, what proportion of viable pregnancies produce children with mutations I would argue is an even more important metric to study.

it is an important metric if it has substance, but according to the above it has very little variance. Knowing how many pregnancies failed versus how many failed prior to the event could give us a better indicator of the damage caused.

I think the question I feel the hive mind wants to answer is, "How much radiation can the species live with and not go extinct". If the birth rates are lower and mortality right is higher we can 'make up' for that. But if the offspring accrue hereditary damage, any amount is too much.

We will have many many tough decisions to make due to the climate crisis.

And it's not just a matter of how much radiation either. Zap a bunch of fruit flies with a dose of x-rays all at once and see the next generation come out horribly mutated. Give them that same dose of radiation over the course of a month and see a perfectly healthy next generation.

Has that happened flies or animals that are immune to high radiation?

I could see the next generation having horrible mutations, I could see the genes correcting some of this in the 3rd generation. I could see some of mutations living on but resistance to radiation would be so extremely useful we would build materials out of them which we are not doing today.

That was my first thought when I saw the title. IIRC roughly 1/3 of pregnancies end within weeks, often before a woman is aware that she is pregnant, almost always because of a genetic mutation. Given that, if the miscarriage rate is higher, that would indicate that there is indeed an impact, but that our genome is very good at preventing dangerous mutations from propagating.

Another possibility is that error-correcting mechanisms are good enough to deal with whatever impact exposure to that level of radiation had. One hypothesis about meiosis and genetic recombination is that it serves as an error correcting process, where damaged genes on one chromosome can be repaired using corresponding genes from the other chromosome.

I was born in August 1986. In northern Poland.

I was born in the 26 pregnancy week. 40 is the avg.

Even if it was not near Chernobyl there were more miscarriage then usual.

So yes looking at the children that survived is not the correct way looking at it.

I also know that getting legit data for that is nearly impossible.

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