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

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 3

What are the odds of conceiving the exact same embryo in these two scenarios?

Here are the two scenarios:

In the first scenario, you conceive an embryo through intercourse. Meanwhile, in the second scenario, you conceive an embryo through in vitro fertilization (IVF). Let's say that the second scenario happens in a parallel universe at the exact same time that the first scenario occurs in this universe.

Anyway, what are the odds that the two embryos conceived in these two parallel universes would be the exact same embryo? Futurist110 (talk) 01:59, 3 October 2018 (UTC)

Depends on who is the father of the child. 86.152.81.16 (talk) 10:21, 3 October 2018 (UTC)

175983257964128056 to 1. — Preceding unsigned comment added by 82.38.221.49 (talk) 12:23, 3 October 2018 (UTC)

An interesting question, but I don't know how you'd get to the answer. I assume from your premise that the gametes in each universe would be identical (otherwise you are asking the usual question of what would have happened if another sperm had won the race). But is there any detectable effect of the procedure? Well, the in vitro fertilization article has two sections about suspected issues ranging from birth defects to hypertension. Whether these are accompanied by any subtler, non-medical change to the offspring is another question. Wnt (talk) 12:40, 3 October 2018 (UTC)

• If you are asking about embryo development differences between IVF and the ol' way, ask it, instead of masking the question in a layer of probability. (I cannot answer that.)

If the real question is about the probabilities that offspring of the same parents has the exact same genetic code... That is the Shannon entropy of offspring DNA. There's a good argument for why DNA entropy is not well-defined but I guess you could easily produce something that looks like a definition; for instance, "for every gene with multiple alleles, estimate the prevalence of each allele, and compute the entropy by assuming genes to be independent (which they obviously are not in reality)". Tigraan^{Click here to contact me} 16:26, 3 October 2018 (UTC)

100% odds, as there is always going to exist a sector within that parallel universe where the required conditions for the exact copy to arise will be met. Count Iblis (talk) 17:34, 3 October 2018 (UTC)

Futurist110, your question does not contain enough information for a proper answer. I am going to fill in some assumptions to try and give an answer. First, I'm going to assume the first-universe embryo is human. There isn't really any reason to expect the second-universe contains humans at all (which would create absurdly astronomical odds), unless humans traveled the other universe or you're just assuming/asserting some sort of clone-universe. In fact I'll assume the egg and sperm come from the same parents (or assumed-clones of the same parents). In that case we can just ignore the parallel universe thing, and just consider two children from the same parents. The use of IVF also does not appear to be relevant.

A human embryo is composed of 46 chromosomes (23 from each parent). For each chromosome, there is a 50-50 chance that the two embryos will inherit a copy of the same chromosome. So the odds are 1 in 2 to the power of 46. That is 1 in 70,368,744,177,664. (One in seventy trillion.) I think this is probably the number you're looking for.

However if we want to consider the possibility of inbreeding, one of the parents could have two copies of the same chromosome. Or the two parents could both have inherited the same chromosome. Each such chromosome would double the chance of producing the same embryo. In particular, if the parents are brother&sister, or mother&son or father&daughter, the chance of producing the same embryo goes up to 1 in 8,388,608. If there are multiple generations of inbreeding, the odds can go much higher.

And if you want to get really technical, I think around a hundred random mutations pop up in the genes each generation. Even identical twins have some small genetic differences due to mutations. Most mutations happen in inactive stretches of DNA and have no effect at all, and most of the rest of the mutations also have no outwardly noticeable effects. It's really only detectable in a pair of identical twins if you do full DNA sequencing for both of them. If you're looking for the equivalent of "identical twins", you probably don't care about those mutations. If you are looking for DNA-analysis-exact-match, you're back to astronomical odds (a number with probably a thousand digits). Alsee (talk) 07:53, 9 October 2018 (UTC)

Inheritance of hair color

I'm interested in under exactly what circumstances a child inherits a specific hair color from its parents. In general, how well understood is the genetics of this? A more specific question is, what hair color would a child of a red-haired father and a blond-haired mother inherit? FreeKnowledgeCreator (talk) 02:33, 3 October 2018 (UTC)

You might find Human hair color helpful. It appears that there are other factors than the visible hair colour that have to be taken into account when attempting such predictions. Richard Avery (talk) 08:51, 3 October 2018 (UTC)

Thank you. It's disappointing to see, however, that the article's section on "Genetics and biochemistry of hair color" is uncited. I'm presuming my more specific question doesn't have a clear-cut answer? FreeKnowledgeCreator (talk) 09:28, 3 October 2018 (UTC)

"There is very little known about hair color inheritance but there are some interesting theories" from The Stanford Department of Genetics.

A better referenced article is Red hair color: The myth from John H. McDonald, University of Delaware. Alansplodge (talk) 12:25, 3 October 2018 (UTC)

A newspaper article from April this year: Scientists discover dozens of new genes for hair colour

The research the article describes seems to be Genome-wide association meta-analysis of individuals of European ancestry identifies new loci explaining a substantial fraction of hair color variation and heritability. Alansplodge (talk) 12:33, 3 October 2018 (UTC)

Does the MRI produce radiation?

I've been under the impression that MRI is dangerous because of a potential radiation exposure. However yesterday I talked to a radiation technician and she said: "No, MRI is all magnetic." I could have found out myself, I want a verification, but it will take longer, so please advise. Thanks. AboutFace 22 (talk) 13:19, 3 October 2018 (UTC)

Have you read our article on MRI? Plenty of verification there. --Shantavira|^{feed me} 13:25, 3 October 2018 (UTC)

If you have concerns about safety, you should ask to speak to the radiologist (who is a medical doctor), not just to the technician who operates the machines.

To clear up the basic physics: an MRI works by emitting and detecting radio-frequency radiation while exposing the test-subject to a powerful static magnetic field. An MRI does emit radiation.

Not all radiation is medically harmful. Review the definition of radiation - the transmission of energy - which takes many forms, including electromagnetic waves of all different types. Consider that ordinary light-bulbs emit large amounts of electromagnetic radiation in the visible light spectrum. Medical harm is caused when the radiation is especially strong, or if it has other special physical properties - like the ability to ionize or otherwise disrupt a material.

Certain categories of radiation are particularly noteworthy for their adverse medical effects on humans: among them are ionizing radiation and the radiation of particles from certain nuclear processes. Broadly speaking, an MRI does not emit ionizing radiation. An MRI does radiate energy in the form of a powerful electromagnetic wave, but it is at a frequency that is generally considered safe for human exposure.

MRIs are classified, by the FDA, as a radiation emitting product. This is accurate from a physical point of view.

Properly-maintained machines are safe and legal for medical use in the United States, subject to many special considerations. In addition to the machine itself, a patient in a normal clinical setting might also be exposed to radiation from other sources at the clinic, including other lab equipment and radiological materials used for diagnostic processes.

One last note: technicians in the clinic are not necessarily experts on the theory of the machine - they are trained in operating it. So, they might not be the best resource for explaining how the machine works.

Nimur (talk) 13:42, 3 October 2018 (UTC)

Or even better, talk to a health physicist (a physicist, not a physician) who understands specifically the medical physics of what the various machines do produce and whether it's a problem. Nor would I undervalue the knowledge of a good operator.

MRI machines do have hazards (magnetism, cryogenics, induced currents), but they're well understood and don't have long-term risks. But (simply put) if you make it in and out of the machine without an obvious accident, you're not going to develop unwanted Superpowers down the line. Andy Dingley (talk) 13:59, 3 October 2018 (UTC)

We have a well referenced and reassuring article Safety of magnetic resonance imaging but there is also in-hospital gossip and sensational reports such as "Man dies after being sucked into MRI scanner at Indian hospital" that serve to maintain awareness of the overriding danger of an MRI scanner which is not radiation but its strong magnetic field that can snatch up a steel Wheelchair with its patient. DroneB (talk) 16:23, 3 October 2018 (UTC)

To the average person, "radiation" means ionizing radiation. Or, more accurately, "scary evil invisible manmade stuff that can KILL YOU AT ANY TIME! RUN AWAY!" --47.146.63.87 (talk) 07:12, 4 October 2018 (UTC)

The average person is under-educated about many things in science: scientific literacy is a real problem in the developed world. For this reason, I think it's preferable to link to reliable encyclopedic resources - like FDA's website - rather than repeating factually-incorrect statements attributable to a generic straw-man. Nimur (talk) 20:15, 10 October 2018 (UTC)

I appreciate the explanations, so the technician was correct. I work at a place where there is an MRI machine, or at least it is my impression, but there are no radiological MD. They transmit images electronically to a large medical center. They simply do not have enough volume. I will find out if they have an MRI machine though. Thanks very much to Nimur, Dingly, DroneB. AboutFace 22 (talk) 16:54, 3 October 2018 (UTC)

They tell you not to bring objects attractable by magnets and electronics that are keeping people alive like pacemakers into the area right? Those are a lot more important than the radiation. Once there was an accident where some idiot turned on the MRI while a steel gas tank (O2? or would that rust like hell or spontaneously explode?) was in the room and it flew towards the magnet and hit the machine at high speed. Sagittarian Milky Way (talk) 18:12, 3 October 2018 (UTC)

You don't "turn on" an MRI machine's magnet. The main magnetic field is either a superconducting magnet, or else (rarely) a permanent magnet using rare earth magnets. Neither of these are switchable. This is why MRI machines are kept in their own rooms (or rooms beyond rooms) and there's a "quarantine" system so that magnetic objects aren't taken beyond the door. When they are, accidents happen. Andy Dingley (talk) 20:49, 3 October 2018 (UTC)

To be pedantic, you don't in normal operation. If things go pear-shaped a magnet quench occurs, which is very expensive. And obviously the machine is shut off in a more orderly fashion for service, to be moved, or whatever. Also for educational purposes: the above poster is discussing how the MRI room is enclosed in a Faraday cage, to contain the field of the magnet as well as keep out interference. --47.146.63.87 (talk) 07:12, 4 October 2018 (UTC)

I remember being told that MRI scanners used to be called NMR scanners (nuclear magnetic resonance) and they changed the name from NMR to MR (I guess MRI was after that) to avoid scaring people with the word "nuclear" (associated with radioactivity). 173.228.123.166 (talk) 00:41, 6 October 2018 (UTC)

Yes, and outside of medicine, "NMR" is still the usual term. --47.146.63.87 (talk) 06:48, 7 October 2018 (UTC)

bug ID

https://postimg.cc/RJnzmp7v

North/Central Europe. Is it parasitoid? Thank you everyone Asmrulz (talk) 13:47, 3 October 2018 (UTC)

Looks like a woodlouse to me. Rojomoke (talk) 15:44, 3 October 2018 (UTC)

Oniscus asellus? Mikenorton (talk) 16:24, 3 October 2018 (UTC)

How far from Earth before the densest air stops being equatorial?

I imagine it might vary somewhat with things like solar activity, time of day and atmospheric tides (perihelionic New Moon perigean spring tides are the strongest and about as far from the atmosphere's equatorial bulge as can be, sometimes both Sun and Moon are equatorial at the same time leaving only the miniscule tides of things like Venus) Sagittarian Milky Way (talk) 18:01, 3 October 2018 (UTC)

Earth atmosphere is not an equally round sphere but more like a drop with a tail in the direction opposite to its orbit vector around the sun, Just like a comet tail but much shorter, because the earth gravitation is way stronger than a comets one. Never the less the "tail" of the Earth actually also causes some Atmospheric escape. Because the Earth axis is slightly tilted and the atmosphere "drop" is shaped mostly by gravity and solar winds, the shape of the atmosphere is not "equatorial" at all. --Kharon (talk) 22:29, 3 October 2018 (UTC)

Maybe Wikipedia could get an article on Equatorial air mass, so users like Kharon would have the opportunity of understanding questions like the one above and spare us all of some nonsense answer. Apart from that, the Air mass article has links in the right direction. Doroletho (talk) 22:47, 3 October 2018 (UTC)

The equaterial air mass occupies the lower Troposphere which extends from sea level to typically a few hundred meters to 2 km (1.2 mi; 6,600 ft) altitude. It is the stagnant air of the doldrums or the equatorial trough, distinguishable from the tropical air of the trade-wind zones (Grimes, A., 1951: Compendium of Meteorology, p. 881). At the altitude of the Tropopause 17 kilometres (11 mi) above equatorial regions, there is virtually no water vapor or variation in weather or temperature, and therefore no part of the mass of the Stratosphere to receive the Bergeron classification Equatorial. DroneB (talk) 17:27, 5 October 2018 (UTC)

vision is by far the most used of the five senses?

I just read a phrase in an ophthalmology book and I'm absolutely not sure about it: "vision is by far the most used of the five senses". Is it really correct? I would say that the hearing or smelling is the most used since they are open involuntarily unlike the eye that at night close as well as many times a day when blinking the eyelids. Isn't it? — Preceding unsigned comment added by 93.126.116.89 (talk) 18:40, 3 October 2018 (UTC)

It is the most used in sense that humans receive more than 90% of information from vision. Ruslik_Zero 20:52, 3 October 2018 (UTC)

Vision records the largest volume of data in humans. In that sense its most used but its not active when we sleep and you wont wake up from light but certainly from sound. So sound is used around the clock without brake. "Most used" is an incomplete quantification because its missing in what regard. Time? Data volume? Sensitivity? --Kharon (talk) 22:44, 3 October 2018 (UTC)

What's the relation between fire and electricity?

I'm looking for differences between fire that comes from an electricity (for example electrical stove) and fire that comes from a real fire. If your religion would tell you that you aren't allowed to use fire for cooking did you used electricity or did you not use it. Kindly let's put aside our opinion about religion at all and try to answer scientifically about the question and give a reason why to resemble or not resemble between the two. I've red a lot of articles on wikipedia and I'm really confused and I believe that great part of it is because I don't have enough (deep) background or 'infrastracture' in sciences. Then please try to explain me in simple words as simple as possible and I'll appreciate it a lot. 93.126.116.89 (talk) 18:52, 3 October 2018 (UTC)

Fire is a rapid chemical reaction in which other elements combine with oxygen to form new molecules consisting of the other elements and the newly-added oxygen. Electricity (in the sense used to create heat) is the passage of electricity through an element that resists, but does not totally block, the passage of electricity. No chemical reactions occur in the electric heating appliance (although chemical reactions may be occurring at the power station where the electricity is being generated). A practical difference is that the gases created during fire are not entirely safe. While a small fire, such as a modern gas kitchen stove, can be used in a room with no planned, active ventilation, a larger fire, such as that needed to heat a house, must be vented to the outdoors with a chimney or equivalent measures. Jc3s5h (talk) 19:01, 3 October 2018 (UTC)

Thank you for your answer. Just to clarify that I understood you answer let me ask something please. you said "No chemical reactions occur in the electric heating appliance". But if I'm not mistaken, physically or microscopically, the eating occurs by the action of electrons moving in the metal very fast and that's what causes heating. isn't it? or maybe I didn't understand your words? 93.126.116.89 (talk) 19:44, 3 October 2018 (UTC)

Electric cookers (with some modern exceptions, such as the microwave oven and the induction hob) work by resistive Joule heating. Electric current in a metal wire flows because the electrons are no longer attached to each atom of the metal but can move quite freely within the metal, between the atoms. They collide with the atoms though, which loses their energy as vibrations, which we then detect outside as heat.

This is not fire though. Fire is a chemical reaction, usually an oxidation and the combination of some fuel with the oxygen in the air as the oxidiser. Each reaction releases a certain amount of energy (this depends on the chemistry involved) and this energy is seen as heat.

Although the end result of both is heat, the mechanisms to produce it are unrelated. Andy Dingley (talk) 20:44, 3 October 2018 (UTC)

A simple Chemical reaction is when two substances combine to produce new substance(s). What we call Fire is commonly the Flame that we see when such a reaction happens to be strongly exothermic (releases heat energy). Familiar examples are whenever a Fuel is consumed by burning in air. Use the links in bold to read more detailed articles. Chemists describe the reactions in burning by equations such as the example below. It describes the burning of hydrogen gas whose end product is simply water; this is a chemist's explanation of the conflagration in the Hindenburg disaster.

2H
₂ + O
₂ → 2H₂O

Be careful with the expression electric fire which in British English means a heating appliance that is powered by electricity. There should be no chemical reaction of fire in such an appliance (room heater, cooker, hairdryer, clothes iron, toaster, etc.) They have internal resistive heating wires made of some metal alloy e.g. Nichrome and this alloy material does not change during the lifetime of the appliance.

Examples of relations between fire and electricity are 1. Electricity in the form of a spark can trigger the start of a fire, as when lightning starts a forest fire, provided there is fuel available for the fire. 2. Fire can be used to heat water to drive a steam generator, thus converting the energy in a fuel to electric power. DroneB (talk) 21:57, 3 October 2018 (UTC)

Chemical reactions can also change a reactant into a simpler substance. Digestion furnishes lots of such examples. As the article says, a chemical reaction involves a transformation of one or more chemicals into other chemicals. There is something of a similarity, at the level of physics, between redox reactions and electric current, since both involve a flow of electrons or other charge carriers, though this doesn't mean they're the exact same thing. Living systems demonstrate this link quite well: your cells produce electric charge gradients by using enzymes to pump ions around, all fueled by the release of chemical energy stored in the food you consume. --47.146.63.87 (talk) 07:26, 4 October 2018 (UTC)

The religious issue you raise can get quite thorny. See Electricity on Shabbat for the example of Orthodox Judaism. --47.146.63.87 (talk) 07:26, 4 October 2018 (UTC)

US Patent no. 7872576 introduces a notion that a manually operated switch whose effect is by design incompletely predictable can somehow reduce the personal responsibility of operating an electric light (said to be a no-no for some Jews on the Sabbath or holy days) or of actions such as discontinuation of life support for terminally ill patients, triggering of a lethal dose in a death sentence, or discharging of a weapon. The article KosherSwitch does not show how this alleged Sabbath-compliant (Shomer Shabbat) device works or address the question of what degree of pseudorandomity is close enough to unpredictable randomity (in the sense of Schrödinger's cat experiment) to impress the God of Abraham as Exculpatory evidence. DroneB (talk) 10:57, 4 October 2018 (UTC)

• Feel free to ask away question about the physics if the above is insufficient. When it comes to the religious law part, I think the correct answer here is the same as for actual law: consult with whoever you feel has actually the authority to make judgement of whether a given course of action is or is not compatible with your religion, rather than asking a bunch of random internet folks. As evidenced by Activities_prohibited_on_Shabbat#Igniting_a_fire, a statement that is scientifically correct ("there is no fire in incandescent light bulbs" is pretty much uncontroversial when "fire" is meant to mean flame) does not necessarily translate into religious rule (at least according to some Orthodox Jew authorities, light bulbs violate the no-fire rule, but of course "fire" in a religious sense might be more than a bunch of chemical reactions). Tigraan^{Click here to contact me} 15:33, 4 October 2018 (UTC)

One way to distinguish fire and electricity is that fire generates waste heat, while electricity is (conceptually, at least) entirely capable of being exploited for work (physics). For example, a coal fired power plant might generate a large amount of heat, but to use this for power generation it must run a boiler or other heat engine which cannot exceed the Carnot efficiency. The remainder of the heat will go out as steam from a cooling tower or warmed water flowing down a formerly cool river. Also, unlike many combustion reactions that are subject to a key temperature threshold (fire point), there is no practical lower threshold for electricity. (Some reactions, such as the hardening of tung oil on a piece of furniture, are essentially a slow, continuous form of combustion; hence rags soaked in that oil can undergo spontaneous combustion in a hot attic) It seems worth noting that small amounts of electricity are always around us - in the nervous systems of people and pets, in static electricity from dry clothes, in eddy currents generated when the magnet holding a cabinet shut is pulled away or put back, or in the corrosion of bimetallic objects that inadvertently become batteries.

That said, there is also a distinction to be made between electricity and a spark made by electricity. Flipping an ordinary light switch produces an electrical arc that has some similarities to fire (other than in not being self sustaining). For example, a room flooded with natural gas might not catch on fire until a light switch is flipped to start the fire (see the distinction between flash point and autoignition point). There is no inherent reason why flipping an electrical switch should produce such an arc; it's just crude design. I don't know much about it, but there are various mentions of arcless electrical switches online, and if a religion were to spur people to redesign their home electrical systems to avoid generating potential ignition sources at any moment in their operation it may not be a bad thing. Wnt (talk) 10:30, 5 October 2018 (UTC)

I know of some Sabbath observers who take the light bulbs out of their refrigerators, so they can open the fridge door on Sabbath without making it turn the light on and off. 173.228.123.166 (talk) 00:45, 6 October 2018 (UTC)

File:Leech crawling.webm

File:Leech crawling.webm is described as a leech, but it looks more like a Bipalium planarian in light of its head. Anyone know what it actually is? Jo-Jo Eumerus (talk, contributions) 19:24, 3 October 2018 (UTC)

Yes, it resembles a Bipalium flatworm. Ruslik_Zero 20:50, 3 October 2018 (UTC)