Wikipedia:Reference desk/Archives/Science/2018 December 3

= December 3 =

More genetics question.
If ignoring crossovers, what's the probability that 2 siblings of the same gender, and different gender, are not related? That is, they each have the other 50% DNA from their parents.

I believe the answer is around (1/2)^23. Because each chromosome sequencing of 2 of 4 possibility is 1/2, then multiple by all the chromosomes. So comes down to 1 in 8,388,608 = .0000119209%.

But the 23rd chromosome determines the gender, so the above answer would be for 2 siblings of different gender. So for 2 siblings of same gender, then the 23rd chromosome is the same, so it's actually (1/2)^22 instead. Am I doing it right?

I have a 2nd question, which is about mitochondrial DNA. I'm curious to know what are some of the obvious differences. For example, when people do DNA testing to determine whether someone is the biological father of a child, or if 2 people are siblings, which DNA testing is done, chromosomal DNA or mitochondrial DNA? Thanks. 67.175.224.138 (talk) 04:35, 3 December 2018 (UTC).
 * Mitochondrial DNA is inherited exclusively from the mother so is completely useless in determining anything about the biological father (well other than aspects of their connection to the mother). While it is useful for Genealogical DNA test, and may be of use when info on the DNA of the person being tested or who they are related to is completely unknown, it's going to be of limited use when the info is known of suspected assuming you have cooperation of all parties. I think it'll generally be difficult to distinguish between siblings (full or half maternal obviously) and maternal-maternal cousin or even the child and their mother and maternal aunts and maternal grandmother etc. Chromosomal crossover means that chromosomes are almost definitely not inherited intact except for the Y chromosome for males and X chromosome from the father for females (as these only undergo very minor recombination). AFAIK it's generally good enough to assume that the genetic similarity between any two full siblings is 50%. I guess the diff BTW this discussion is loosely related Reference desk/Archives/Science/2017 September 9. Nil Einne (talk) 05:41, 3 December 2018 (UTC)
 * Yes, you just can't ignore crossovers. And more specifically, when people do DNA testing to determine whether someone is the biological father of a child, or if 2 people are siblings, the bulk of the testing is on autosomal DNA. - Nunh-huh 05:54, 3 December 2018 (UTC)
 * Regarding the 2 siblings are generally assumed 50%, I've seen the standard deviation models that say 3-4%. That is, 47-53% or 46-54% which will cover like 99% of the population. I also saw a person respond on Quora that 37% is like a record deviation but I haven't seen anything or article to convince that. 67.175.224.138 (talk) 06:06, 3 December 2018 (UTC).
 * The 37% figure may have come from this . It's an interesting paper but, perhaps not surprising given when it was done, it seems to rely on between 201 to 1,717 genetic markers (with the various assumptions etc necessary to calculate the results. I think this touches on a significant issue namely 'what do you mean by 37% similar'? Nil Einne (talk) 08:54, 3 December 2018 (UTC)
 * P.S. I was going to write some like this in an edit to my original reply but abandoned that however it seems I forgot to remove my initial addition. "I guess the probably difference is more than one percent so 50% is probably not entirely accurate, but in most scenarios it isn't considered. I'm also doubtful that it's easy to calculate a priori, you'll probably be far better off looking at genomic data." Nil Einne (talk) 09:08, 3 December 2018 (UTC)


 * You have 23 chromosomes, but you always get one from both of your parents, so that gives 46 total. Siblings of the same gender always have the X or the Y chromosome from their father in common, so they are related in your words. If they have different gender, we can ignore the X or Y chromosome from the father. The probability of these siblings having unrelated DNA is then (1/2)45 or about 1 in 3.5⋅1013. But, as stated above, you can't ignore crossover. PiusImpavidus (talk) 09:15, 3 December 2018 (UTC)
 * Nope, there is also X-Y crossover, in the Pseudoautosomal region. Indeed, according to that article "crossing over (recombination) between their pseudoautosomal regions appear to be necessary for the normal progression of male meiosis.[13] Thus, those cells in which X-Y recombination does not occur will fail to complete meiosis."  So, not only is it possible for some crossover between X and Y chromosomes, it is actually necessary for normal meiosis.  -- Jayron 32 17:21, 3 December 2018 (UTC)

gravity on other bodies: confirmed?
The surface gravity of the Moon, Mars etc. was calculated long before anything landed there, but has any lander bothered to measure it? For example, did any Apollo crew measure the period of a pendulum? —Tamfang (talk) 08:29, 3 December 2018 (UTC)


 * I wonder how successful the moon landing would have been if there was a significant error in their estimate of g? Greglocock (talk) 08:42, 3 December 2018 (UTC)


 * Gravimeters using special springs rather than pendulums were invented in the 1930's by Lucien LaCoste. We have been measuring the effects on local gravity of Mascons on the Moon since 1968 from spacecraft and probes orbiting it (a recent mission is described here), and such measurements have been made on Mars as well. I don't know if gravitometers have been carried on specific landers, but doubtless someone else will be able to enlarge on this. {The poster formerly known as 87.81.230.195} 90.202.210.56 (talk) 10:02, 3 December 2018 (UTC)


 * Wikipedia has an article titled Gravity of Mars which includes both earth-based estimates from observations, and measurements made by probes, landers, etc. as early as Mariner 9. There are several other probes and landers which made measurements listed in the article as well.  -- Jayron 32 11:51, 3 December 2018 (UTC)

Yes, confirmed by measurements of tides the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of Earth as long ago as the 2nd century BC by the Babylonian astronomer, Seleucus of Seleucia who was the first to link tides to the lunar attraction. DroneB (talk) 15:06, 3 December 2018 (UTC)
 * This answer does not appear to address the OP's question in any way. {The poster formerly known as 87.81.230.195} 90.202.210.56 (talk) 11:21, 4 December 2018 (UTC)


 * Regrettably, the Lunar Surface Gravimeter, carried to the Taurus Littrow valley on the Moon's surface by the astronauts of the Apollo 17 mission, "failed" due to a manufacturing defect. No useful science data was collected by that instrument, but it would have yielded highly-accurate and time-varying measurements of lunar surface gravity, if it had worked correctly.
 * This instrument was not a pendulum, but was a mass-spring instrument similar to the Lacoste-Romberg gravity meters commonly used by geoscientists on Earth.
 * If you're interested in its operational details, here is a 1972 training hand-out prepared to familiarize Earthling scientists with the instrument package so they could analyze its data in "post-production."
 * Needless to say, there have been plenty of other, less-accurate--but-still-pretty-accurate measurements of Moon's gravitational field - mostly from orbital instruments and orbital-mechanics calculations relating to orbital navigation. For example, Apollo 15 released its "Sub-Satellite, which accurately measured Moon's gravity from orbit.
 * Nimur (talk) 17:17, 3 December 2018 (UTC)
 * Yes, not only have individual point measurements been taken, but the force of gravity has been mapped across the entire surface of bodies such as the moon. It has been determined from this data that concentrations of mass exist within the moon, which are referred to as "mascons". In fact, before these accurate gravitational surveys had been conducted, probes orbiting the moon experienced unexpected perturbations to their orbits that caused them to crash after few orbits than expected, such as the case of PFS-2. 202.155.85.18 (talk) 05:57, 6 December 2018 (UTC)

Fate of dead bacteria.
So I think this planet is being filled with dead bacteria and is not as reversible. Do bacteria eat dead bacteria? If not, then hence my conclusion. When you pour concentrated bleach on your floors, that kills living bacteria (and therefore takes away it's smell, which is an accomplishment). When the janitor mops the bleached floor, he moves dead bacteria around, and only some of it getting into the janitor's bucket via the mop which is eventually poured into the sewers. I also heard some dead bacteria end up being broken further down into proteins, carbs, and nucleic acids. (It's not like you can use a gigantic vacuum cleaner and vacuum it all up.). And matter can't be destroyed. Now for the dead bacteria that goes into sewers: it is also safe to drink water with dead bacteria - say, after boiling it to 165 F and cooling it back down. We cook meat and then eat the meat with the now-dead bacteria. My toxicology textbook says fecal matter is about 30-42% weight originating from bacteria. And some dead bacteria is shower-rinsed, so that along with toilet, all goes to a sewer system. So what about in the treatment plant in the 2ndary treatment, where the bacteria eat the sewage - is that were bacteria eat some dead bacteria? Notes: the cell wall of bacteria is peptidoglycan - article says peptidoglycan makes up 90% of weight of Gram-positive bacteria and 10% of weight of Gram-negative bacteria, so this planet is also being filled with peptidoglycan molecules too, which I guess can be broken down. Thanks. 67.175.224.138 (talk) 17:19, 3 December 2018 (UTC).
 * Sorry, your question is a bit scrambled; so I'm having trouble following it. Best as I can make out, your question is what is the harmfulness of bacteria already dead compared to living bacteria.  Many bacteria are only harmful while they are alive, but there ARE some bacteria that leave residual toxins which do not decompose, and could harm you even if the original bacteria are dead.  The most famous example I can think of is Clostridium botulinum, which produces Botulinum toxin.  The toxin can cause Botulism even if the original bacteria is dead; though the toxin is denatured by cooking above a certain temperature, and/or treatment with some kinds of disinfectant chemicals.  I hope that at least partially answers your question.  -- Jayron 32 17:35, 3 December 2018 (UTC)
 * Yea I think there's 2 types of toxins you're talking about: endospores and exotoxins. 2 main types of endospores come from Gram-positive bacteria are from the aerobic Bacillus and the anaerobic Clostridium. Then exotoxins are proteins released by both Gram-positive and negative bacteria. E. coli, Vibrio, Shiegella, all release them. Examples of diseases caused by bacterial exotoxins include anthrax, botulism, tetanus, and cholera. Does anyone know if it's safe to eat dead exotoxins? Now there is a 3rd category but it is not a spore, this 1 being endotoxins, which is a piece of outermembrane of Gram-negative bacteria. 67.175.224.138 (talk) 15:47, 4 December 2018 (UTC).
 * What do you mean by "dead"? If a toxin has been properly chemically altered, it isn't that toxin anymore.  For example, bleach is a good general-purpose oxidizer that massively disrupts most organic molecules, many toxins are effectively destroyed by bleach, others by heat, etc.  These are not "dead", they were never "alive", but it is more accurate to say they have been chemically altered into new substances that aren't harmful anymore.    -- Jayron 32 16:10, 4 December 2018 (UTC)
 * Note also that chlorine bleach is quite good at reacting with organic substances and converting them to carbon dioxide. But also you will be eating tiny amounts of bacteria live and dead all the time without harm. Many small animals also eat bacteria, these would include mites and worms in terrestrial environments. In water many things eat bacteria, eg protozoa and filter feeders. One result of rotting down organic matter is compost or humus which will be rich in dead bacteria. Accumulation of dead bacteria is reversible, and almost everything produced by living organisms is consumed by another living organism. Graeme Bartlett (talk) 21:37, 3 December 2018 (UTC)


 * Dead bacteria are part of the organic component of soil, where they are consumed/absorbed and broken down by living organisms including bacteria, plants, fungi and animals.- gadfium 22:17, 3 December 2018 (UTC)


 * Plants dominate the total biomass, bacteria come second, so most of the dead bacteria are recycled as plants. Count Iblis (talk) 04:50, 4 December 2018 (UTC)
 * Your gut and skin are entire ecosystems filled with things that live, reproduce, and die. Everywhere on Earth where life can exist is filled to the brim with bacteria and other microbes. We are just one part of a living, breathing, biosphere. Every glass of water you've ever drank had bacteria in it, whether from the container, the air, or the pipes. "Recycling" organic molecules is pretty much what organisms do, and indeed, most dead bacteria are "eaten" by other bacteria. Without bacteria decomposing the remains of organisms, we would be buried in waste almost overnight.
 * On a specific note about bleach: bleach gets rid of many odors by oxidizing the chemicals that smell. Killing microbes is only tangentially related, in that, obviously, if bacteria are producing odoriferous compounds, killing them will stop them from making more. These smells are most often thiols produced by bacteria breaking down sulfur compounds; a widespread example is hydrogen sulfide, which has the distinctive "rotten egg" smell. --47.146.63.87 (talk) 08:56, 4 December 2018 (UTC)
 * So you think dead bacteria for the most part smell the same as living bacteria? The analogy I use here is washing feet, because overtime feet smells due to the increased presence of anaerobic bacteria, rinsing feet with water rinses off some of them. 67.175.224.138 (talk) 15:47, 4 December 2018 (UTC).
 * Bacteria don't really "smell". When you smell something, you're detecting molecules that are binding with olfactory receptors in your nose. Generally these are volatile molecules, like the aforementioned hydrogen sulfide. Bacteria aren't molecules; your nose doesn't have smell receptors for bacteria. Bacteria can release compounds into the environment that you can then smell, but, to me, that isn't the same thing. If your feet smell, it's not that bacteria from your feet are wafting into the air and into your nose. The bacteria adhere to your skin. What you're smelling are volatile odor compounds produced by the bacteria as they digest your sebum, sweat, and dead skin. --47.146.63.87 (talk) 20:06, 4 December 2018 (UTC)

Where can I find US TV reception maps from before the analog shutdown?
Google is overgrown with sites giving post-2009 maps. Sagittarian Milky Way (talk) 21:41, 3 December 2018 (UTC)

What do space engineers/planners say is the best approach for the immediate future, and is manned exploration part of it?
Background(as I perceive it): Humans went to the Moon, but then Moon exploration fizzled, maybe because of the lack of payoffs that needed to be both obvious and huge, so enthusiasm went down. Then we decided to focus on manned space stations orbiting Earth, closer to home, and thus (we hoped) more practical, and economic. But my perception, and also my perception of the perceptions of the taxpaying public, is that space stations haven't had many payoffs scientifically or economically either-we just do it for the sake of international comity and the fun of putting "athletes" up there. Now the discussion is on should we do a manned mission to Mars and/or put colonies(akin to manned space stations, in a way) on the Moon, but much as I would like those, the arguments in favor don't seem to be any different than the arguments for the first manned trips to the Moon or the space stations-it seems to be mainly arguments for how inspiring it would be. And I don't want us to have another fizzling of enthusiasm...Meanwhile, my other perception is that NASA and other nations' space agencies and private companies have been doing and are doing a great deal of worthwhile scientific, profitable, and military stuff up there with unmanned machinery.-so Q1.] Is anything really reachable with current tech out there that humans with current life support and propulsion systems could learn from or make profitable?(vs what unmanned machines/robots could do)? Q2.] If not, should we focus on unmanned exploration? Just for now, or forever? Q3.] Will manned exploration ever be no more difficult than Columbus's admittedly difficult journey to the Americas? Because going to the Americas made money and led to scientific advances.(Would fission or fusion rockets be enough to make that happen, or do we need something totally new?) What I would like is for my perceptions to change by getting information from you that space experts think there's a quadrillion bucks to be made out there on the Moon, and that going to Mars isn't crazy, and not purely inspirational in motive. Links would also be appreciated! ThanksRich (talk) 21:56, 3 December 2018 (UTC)


 * I've linked this 2015 speech several times: Astronomy Talk: America’s Space Program – NASA’s Roadmap To Tomorrow’s Missions, in which former NASA Administrator Charles Bolden candidly describes, well, NASA's roadmap. Dr. Bolden is a scientist, astronaut, pilot, and an expert in spaceflight policy; he directly addressed almost all of the questions posed here during that invited talk at the Keck Observatory.
 * Since that time, we've had a change of president, which has also meant a change in space policy.
 * If you want something slightly more recent, here's the 2017 Space Policy Directive from December 2017; and here's Space Policy Directive #2 from May 2018; and here's Space Policy Directive #3 from June 2018.
 * ...And here's another interview with Charlie Bolden from summer 2017 - after he stepped down - in which he can speak with even more candor about spaceflight and its future.
 * Nimur (talk) 00:59, 4 December 2018 (UTC)
 * If the Soviets got lucky enough to do JFKs goal first America would've tried to do something harder. Sagittarian Milky Way (talk) 17:26, 4 December 2018 (UTC)
 * ...Probably not... If you want some context for the history of JFK's announcement, here's a very wonderful 1979 documentary, The other side of the moon, presented by historian James Burke who covered the Apollo Program for BBC. President Kennedy's bold public statements announcing our moon aspirations were the result of many years of diligent behind-the-scenes research.  Unlike more recent presidents, Kennedy did not make his remarks "off the cuff."  His advisors did a lot of homework to make sure the President did not make a statement that would be later proven impossible - because in the early 1960s, Presidents of the United States refrained from loose talk and foolish statements.  Nimur (talk) 03:04, 5 December 2018 (UTC)