Wikipedia:Reference desk/Archives/Science/2019 December 3
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December 3[edit]
atmospheric mercury[edit]
[1] Atmospheric mercury in the fog is poisoning pumas in the Santa Cruz mountains. "The neurotoxin [mercury] is coming out of the ocean through a process that happens in the deep ocean involving mercury."
What is this process dumping mercury into the air from the ocean? Is it a natural and steady process, industrial, natural and worsening from global warming, or what? Does the mercury concentrate in water vapor like fog? Will it get strong enough to affect humans, if it's not affecting us already? This is the first I've heard of this. Thanks. 67.164.113.165 (talk) 06:20, 3 December 2019 (UTC)
- The mercury that this is about is not in the air itself (although air can contain elemental mercury); it's organic mercury compounds in the water droplets making up the fog. Here is the original paper from Nature. If the paper talks about the details of formation of contaminated droplets, I missed it on a quick skim. Anyway, Figure 5 may be of particular interest. --76.69.116.4 (talk) 07:24, 3 December 2019 (UTC)
Genetics and probability[edit]
Given two female cousins - who have only one common grandfather yet no common grandmothers - and who have only uncles yet no aunts, what's the probablity of those cousins to be genetically "unrelated", if neither cousin's mother nor cousin's father's mother are genetically "related" to each other (as far as women of Homo-sapiens can be genetically "unrelated")?
By the way, of course we can disregard the allosomes (gonosomes), because those of the cousins - are genetically "unrelated" - necessarily (per the given data). 87.70.13.99 (talk) 16:13, 3 December 2019 (UTC)
- If they truly have one grandfather in common, then basically zero. Are you under the mistaken impression chromosomes are inherited intact or as a whole unit? They are not. See genetic recombination. Nil Einne (talk) 17:27, 3 December 2019 (UTC)
- If by "basically" (zero) you mean "almost" (zero), then I agree, but I'm asking about this low probability that is - very close to zero - yet not absolutely zero. 87.70.13.99 (talk) 17:48, 3 December 2019 (UTC)
- See the definition of basically zero ? --Askedonty (talk) 18:49, 3 December 2019 (UTC)
- Your link doesn't mention the term "basically zero". Anyway, I'm speaking about a probability that is - very close to zero - yet not absolutely zero (just as the rest mass of electron is - very close to zero - yet not absolutely zero, as opposed to the rest mass of photon that is absolutely zero). 87.70.13.99 (talk) 19:04, 3 December 2019 (UTC)
- Precisely: "extremely low (but technically not zero)". Read the article. --Askedonty (talk) 19:15, 3 December 2019 (UTC)
- The term you have just used, is by no means more precise than the term I had used ("very close to zero"). Anyway, I had been referring to the term "basically zero", rather than to the other term you have just used. 87.70.13.99 (talk) 19:24, 3 December 2019 (UTC)
- Actually, the better link from a probability standpoint is almost never, which is a precisely defined term in probability theory. It includes any result which real results, but none-the-less will never happen. For example, there is a real result in the above scenario has real solutions. It is technically possible to build two identical genomes from first principles. You simply need to order the nucleotides of the DNA the same way in both people. That is a real thing; the probability of which is happening is so functionally low as to be almost never happening. What this means is not "this might actually happen" what it means is, although there are real solutions that have this result, it actually never happens from a probabilistic standpoint. Terms like "basically zero" are also used for "almost never" and mean the same thing. In simplest terms, something can re a real result, and still have a probability of almost never happening. The result described by the OP fits that definition. The link provided by Askedonty is a similar concept, but was too oblique a relationship. Almost never is the correct concept from statistics. --Jayron32 20:44, 3 December 2019 (UTC)
- I don't disagree with anything you said but note that the OP was asking about 2 genomes being "unrelated" not identical. I guess in the context of their question, this would imply every part of their genome just happened to come from one of their other grandparents by chance. Nil Einne (talk) 21:08, 3 December 2019 (UTC)
- Yeah, sorry I wasn't clear. It almost never will happen that two such cousins will have completely dissimilar genetic codes. They will almost surely have genetic codes which are very close to the predicted relatedness; and will almost never have DNA which shows any significant variation from that, almost surely not zero relatedness. In terms of statistics, the terms "almost never" and "almost surely" means that, while the result of "zero relatedness" is a real result, there is no chance of it happening, indeed there is very slim chance of any result outside of some small window around the predicted statistics. That is because the law of large numbers is at play here. There are a stupidly large number of genes and a stupidly large number of chromosomal crossover events that actual offspring basically almost surely match the predicted results. --Jayron32 21:24, 3 December 2019 (UTC)
- I guess the hypothesis of the OP could be elaborated on the Law of independent assortment but I'm leaving it there as to putting numbers behind the number of characters to be slalomed between within the course of four generations, to try getting at the hypothesis. --Askedonty (talk) 21:59, 3 December 2019 (UTC)
- Yeah, sorry I wasn't clear. It almost never will happen that two such cousins will have completely dissimilar genetic codes. They will almost surely have genetic codes which are very close to the predicted relatedness; and will almost never have DNA which shows any significant variation from that, almost surely not zero relatedness. In terms of statistics, the terms "almost never" and "almost surely" means that, while the result of "zero relatedness" is a real result, there is no chance of it happening, indeed there is very slim chance of any result outside of some small window around the predicted statistics. That is because the law of large numbers is at play here. There are a stupidly large number of genes and a stupidly large number of chromosomal crossover events that actual offspring basically almost surely match the predicted results. --Jayron32 21:24, 3 December 2019 (UTC)
- I don't disagree with anything you said but note that the OP was asking about 2 genomes being "unrelated" not identical. I guess in the context of their question, this would imply every part of their genome just happened to come from one of their other grandparents by chance. Nil Einne (talk) 21:08, 3 December 2019 (UTC)
- Actually, the better link from a probability standpoint is almost never, which is a precisely defined term in probability theory. It includes any result which real results, but none-the-less will never happen. For example, there is a real result in the above scenario has real solutions. It is technically possible to build two identical genomes from first principles. You simply need to order the nucleotides of the DNA the same way in both people. That is a real thing; the probability of which is happening is so functionally low as to be almost never happening. What this means is not "this might actually happen" what it means is, although there are real solutions that have this result, it actually never happens from a probabilistic standpoint. Terms like "basically zero" are also used for "almost never" and mean the same thing. In simplest terms, something can re a real result, and still have a probability of almost never happening. The result described by the OP fits that definition. The link provided by Askedonty is a similar concept, but was too oblique a relationship. Almost never is the correct concept from statistics. --Jayron32 20:44, 3 December 2019 (UTC)
- The term you have just used, is by no means more precise than the term I had used ("very close to zero"). Anyway, I had been referring to the term "basically zero", rather than to the other term you have just used. 87.70.13.99 (talk) 19:24, 3 December 2019 (UTC)
- Precisely: "extremely low (but technically not zero)". Read the article. --Askedonty (talk) 19:15, 3 December 2019 (UTC)
- Your link doesn't mention the term "basically zero". Anyway, I'm speaking about a probability that is - very close to zero - yet not absolutely zero (just as the rest mass of electron is - very close to zero - yet not absolutely zero, as opposed to the rest mass of photon that is absolutely zero). 87.70.13.99 (talk) 19:04, 3 December 2019 (UTC)
- See the definition of basically zero ? --Askedonty (talk) 18:49, 3 December 2019 (UTC)
- If by "basically" (zero) you mean "almost" (zero), then I agree, but I'm asking about this low probability that is - very close to zero - yet not absolutely zero. 87.70.13.99 (talk) 17:48, 3 December 2019 (UTC)
- See user:eric's comment below, followed by my response. 87.70.13.99 (talk) 23:34, 3 December 2019 (UTC)
- On my part the avantage of my link is that it deals with text strings and that's reputedly very similar to DNA. --Askedonty (talk) 21:11, 3 December 2019 (UTC)
- (ec) Doesn't that article say that the probability has to equal 0 to be "almost never"? An infinite number of coin flips will "almost never" be all tails? A finite number of coin flips being all tails has a probability greater than 0, and is not "almost never".—eric 21:17, 3 December 2019 (UTC)
- Correct, and that's why I (the OP) asked my question, which is more analogous to a question about a finite (rather than an infinite) number of coin flips being all tails. 87.70.13.99 (talk) 23:34, 3 December 2019 (UTC)
- Is this even getting into the territory of "virtually zero" or "basically zero"? Based on a less than high school understanding of genetics and the premises there is a fairly high probability that any one pair will be unrelated. And can you just raise that to the power of 22? Anyone who knows more got a napkin handy?—eric 15:53, 4 December 2019 (UTC)
- The point is, there isn't much use in entertaining the possibility of events where the math makes it clear that there is not an expected result to occur like that until long after the heat death of the universe. Anyone with a modicum of understanding of the fantastically large numbers involved doesn't spend the intellectual energy necessary to consider such "probabilities" as worth the time and energy to compute, let alone consider a real chance. You can get a number, if you wanted to. I'll concede that the number you get is more "not meaningfully enough larger than zero without invoking false precision to be useful to draw conclusions with" rather than "honest-to-god-actually zero", though the former can be safely called "zero" without any meaningful difference to understanding the concepts at hand. Just because you can do math and get a number doesn't make it a useful number. --Jayron32 16:30, 4 December 2019 (UTC)
- Sorry for hijacking the thread, but let me try and ask another way. If crossover happens all the time, or almost all the time, chances are in the "heat death of the universe" range. If crossover happens only most of the time, chances start to get better. Almost all search results are for genetic algorithms, not genetics, and can give some pretty low values. Is it as this page from Stanford implies: "You didn't get any whole chromosomes from either parent", or maybe say a 20% chance you end up getting a whole chromosome? Crossover value and Chiasma (genetics) don't help much.—eric 19:43, 4 December 2019 (UTC)
- The point is, there isn't much use in entertaining the possibility of events where the math makes it clear that there is not an expected result to occur like that until long after the heat death of the universe. Anyone with a modicum of understanding of the fantastically large numbers involved doesn't spend the intellectual energy necessary to consider such "probabilities" as worth the time and energy to compute, let alone consider a real chance. You can get a number, if you wanted to. I'll concede that the number you get is more "not meaningfully enough larger than zero without invoking false precision to be useful to draw conclusions with" rather than "honest-to-god-actually zero", though the former can be safely called "zero" without any meaningful difference to understanding the concepts at hand. Just because you can do math and get a number doesn't make it a useful number. --Jayron32 16:30, 4 December 2019 (UTC)
- Is this even getting into the territory of "virtually zero" or "basically zero"? Based on a less than high school understanding of genetics and the premises there is a fairly high probability that any one pair will be unrelated. And can you just raise that to the power of 22? Anyone who knows more got a napkin handy?—eric 15:53, 4 December 2019 (UTC)
- Correct, and that's why I (the OP) asked my question, which is more analogous to a question about a finite (rather than an infinite) number of coin flips being all tails. 87.70.13.99 (talk) 23:34, 3 December 2019 (UTC)
- On average, half first cousins share 457 centiMorgans (cM) of genetic material, and the observed range is 137 to 856 cM. [3]. If you enter 0 as the number of shared centiMorgans you can see at what level of relationship that has been observed - generally on the order of 3rd cousins. - Nunh-huh 22:38, 10 December 2019 (UTC)