Wikipedia:Reference desk/Archives/Science/2012 August 29

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August 29

Kepler-47

The caption on image 6 of this image gallery about Kepler-47 reads: "This screenshot from a NASA animation shows the orbital paths taken by the two known planets in the Kepler-47 system, which both orbit the same two stars." That last part seems intriguing to me. Do we know of an example where two planets in the same system orbit different stars? Dismas|^(talk) 00:26, 29 August 2012 (UTC)

My understanding was that the separate orbiting of one star in a binary system was the norm, and this "tatooine" situation was notable because it was the first confirmed where a planet orbited both binaries. μηδείς (talk) 02:59, 29 August 2012 (UTC)

The binary stars HD 20781 and HD 20782 have 2 and 1 confirmed exoplanets respectively. The binary stars HD 11964 and HD 11977 have 2 and 1 confirmed exoplanets respectively. Since these are wide-binaries, astronomers classified them as separate systems, so technically the answer to your question would be no.

In case a similar question comes up again in the reference desk, I found the answer by going to List_of_exoplanetary_host_stars, sort the table by the number of confirmed planets, and then shift-cliking every yellow row. Then I just do a ctrl-f for "binary" in each new tab.A8875 (talk) 03:54, 29 August 2012 (UTC)

Superheating and nucleation

From the superheating article: "Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid. ... Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure – the atmospheric pressure, primarily. Below that temperature, a water vapor bubble will shrink and vanish. Superheating is an exception to this simple rule: a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles."

I have three questions: 1) what are the usual nucleation sites in a "regular" pot of water that cause it to boil at 100C? Irregularities in the surface of the pot which trap pockets of air are one. Are there any others? 2) how do these nucleation sites actually promote bubble-making. (I don't see how trapping air will make it easier to form bubbles). 3) why do these bubbles only need to overcome the ambient pressure, and not the ambient pressure + pressure due to surface tension?

Thanks. 65.92.7.148 (talk) 00:57, 29 August 2012 (UTC)

Also, in bubble chambers, why doesn't the sudden formation of bubbles cause the whole thing to boil? 65.92.7.148 (talk) 01:01, 29 August 2012 (UTC)

Metal pots likely have LOTS of good nucleation sites, metals have a crystal structure and at the microscopic level are rarely very smooth, regardless of how they feel. It is almost impossible to superheat a liquid in a metal container for this reason. Amorphous solids like glass, that lack a crystal structure, make better containers to superheat a liquid in because they are truly smooth, and so lack nucleation sites. How nucleation sites work is explained in some detail at Nucleation, but the (over)simplified version is that nucleation sites provide a place for bubbles to collect roughly the same way that surface catalysts do: they provide a mechanism which lowers the activation energy necessary to make the transition from the liquid to the gas phase. In super simple terms: they give bubbles something to cling to while they form. Once a tiny bubble forms, it creates a surface; smaller bubbles have a greater surface tension per unit volume than larger ones do (that's because surface area grows as a square function but volume as a cubic function, so as the volume goes up by a factor of 1000, the surface area only goes up by a factor of 100, and the gap between the two gets bigger as the size continues to increase). That means the greatest surface tension exists for the smallest possible bubbles, and their just isn't enough gas inside these bubbles to exert enough pressure against the surrounding liquid to overcome their own surface tension, so they collapse on themselves and never grow. Nucleation sites basically break up the surface tension of these nacent bubbles, giving them the opportunity to form a stable bubble and float to the surface. --Jayron32 03:02, 29 August 2012 (UTC)

Thanks. In bubble chambers, ions apparently act as nucleation sites. Any idea how that happens?

Also, I'm looking for a text to brush up on the physics of phase transitions. I realized I have (pretty much) no idea what's "going on" when, for example, water starts to boil. Any recommendations? 65.92.7.148 (talk) 00:17, 30 August 2012 (UTC)

See symmetry breaking. Any sort of balanced high-energy system will collapse given the slightest chance to do so. You don't need to shake a balanced pin very hard to get it to fall over. μηδείς (talk) 01:30, 30 August 2012 (UTC)

Mars Science Laboratory Flight Path

Hi, I'm looking for the Curiosity Rover's flight path, something similar to this:

I checked the Mars Science Laboratory article and some of the related articles (like the timeline), but I can't seem to find it. Basically, I want to see the placement of the Earth & Mars during the takeoff & landing, and view the orbit of the planets while also keeping track of Curiosity's position, all of this relative to the Sun.

A snapshot of the celestial bodies' positions at takeoff, and a separate snapshot of the celestial bodies' at landing, would be helpful, but what I'm looking for is either an animation, or month by month snapshots at least.

Any help is appreciated, thanks!--99.179.20.157 (talk) 03:48, 29 August 2012 (UTC)

You can quickly estimate this via any Hohmann transfer orbit image, such as the one here. Most of them (like this one) are going to show you Earth position at launch and Mars position at landing, but it's pretty easy to extrapolate the rest. A ~230 day flight means that Earth has moved approx 2/3rds around its orbit by the point of landing, and that Mars needs to be backed up approx 1/3rd around its orbit to show the correct position at launch time. The speeds of both planets and the spacecraft can be reasonably approximated as constant. — Lomn 04:26, 29 August 2012 (UTC)

One way to watch the flight is JPL's Eyes on the Solar System (Java in browser required). Enter the launch date in Date+Time and use Speed+Rate to fly forward and backward in time. Click the spacecraft's name to center on it, and use the mouse to rotate the view, and just play with the controls. You can also see a quick demo at TED.

There are other planet position simulators, search the web, e.g. [1] - won't show the spacecraft but you can move in time from launch date to landing to see how the planets moved. 88.112.47.131 (talk) 11:46, 29 August 2012 (UTC)

For a simple image, see here (scroll down to bottom): http://www.dangl.at/2011/msl/msl_e.htm --99.227.95.108 (talk) 05:22, 1 September 2012 (UTC)

professions

I've been reading these helpdesk answers for years and there are such brilliant replies. Which of the 'regulars' here actually work as scientists or as teachers/professors? I'm not looking for stats but just some short replies from the regulars. Thanks. Sandman30s (talk) 06:57, 29 August 2012 (UTC)

I used to be a freelance lecturer in colleges and universities in the UK. Now retired through ill health. --TammyMoet (talk) 08:11, 29 August 2012 (UTC)

Rocket scientist. --Stone (talk) 08:18, 29 August 2012 (UTC)

You left out an important class of knowledgeable people - Engineers. I started my career in Electronic Engineering, then when Govt policy killed off the Electronics industry in Australia, I worked in IT as a software Engineer & project manager, then became a diesel power generation Engineer. I have multiple diploma and degree level qualifications. Now semi-retired as in Australia if you are over 65 you can't be covered by accident insurance at work. I still do some consulting, and I'm also doing research. Ratbone121.215.24.39 (talk) 10:12, 29 August 2012 (UTC)

It wasn't intentional... also if you throw in engineers then there are many other classes who would regard themselves just as knowledgeable :) I was more interested in the academic/educational professions. Engineers are more than just academic... Sandman30s (talk) 11:31, 29 August 2012 (UTC)

I currently work as a scientist, and have also worked as a university lecturer. SemanticMantis (talk) 12:43, 29 August 2012 (UTC)

I'm a library technician, but I can't provide any published references to prove it. Mingmingla (talk) 20:21, 29 August 2012 (UTC)

I'm a chemistry teacher by training and exprience, but I am currently (voluntarily) not doing that. I am mostly a stay-at-home parent, and will be until my youngest child is in school. I do work some as a private tutor to keep active. --Jayron32 20:29, 29 August 2012 (UTC)

I have found that identifying yourself honestly at wikipedia (check my name at wiktionary) leads to being stalked and persecuted by rather disgusting partisan creeps, so I haven't chosen to come anywhere near my post www identity. Suffice it to say I am a credentialed professional with teaching and commercial experience and a love thereof. μηδείς (talk) 05:32, 30 August 2012 (UTC)

I own an aluminum baseball bat. --Jayron32 05:41, 30 August 2012 (UTC)

Do you discuss certain...nontraditional uses...of that on usenet? Or are you mentioning it here in terms of defense rather than previous online identities? DMacks (talk) 13:50, 30 August 2012 (UTC)

I'm a geological consultant and former university researcher (I'm more of a semi-regular here). Mikenorton (talk) 18:12, 30 August 2012 (UTC)

I've taught CAD. StuRat (talk) 03:25, 31 August 2012 (UTC)

General anaesthesia

Normally when general anaesthesia is administered to a patient, there is a lot of preparation before hand such as assessments, emptying bowels, ensurin the patient doesn't eat or drink before hand etc but how is all this done in emergency surgery in life threatening cases where patients are taken straight to surgery from emergency. Also are relaxants etc used before general anaesthesia to relax patients? Clover345 (talk) 10:56, 29 August 2012 (UTC)

Obviously they make do with what they can do. Emptying the stomach, for example, is to keep the patient from involuntarily vomiting and perhaps choking during the procedure. If you can get them to not eat anything before the procedure, it's one less thing for the anesthesiologist et al. to worry about. If you can't, it's one more thing for them to worry about. You don't let the perfect be the enemy of the good when dealing with emergencies. I've no clue about relaxants used before general anesthesia, but I have experienced cases of relaxants being used before local anesthesia, for whatever that is worth. --Mr.98 (talk) 12:36, 29 August 2012 (UTC)

It's common practice to administer a tranquilizer before general anesthesia -- see General anesthesia#Premedication. Looie496 (talk) 17:57, 29 August 2012 (UTC)

It is a question of relative risks. I have been anesthetized and sedated twice upon emergency room admission. The diagnosis was severe enough and the need to treat me so obvious that waiting for me to fast was not an option. That is for elective surgery. μηδείς (talk) 05:38, 30 August 2012 (UTC)

Come to think of it, they did pump my stomach on the second occasion they sedated me, since emergency abdominal surgery was indicated. μηδείς (talk) 16:34, 31 August 2012 (UTC)

Carl Linnaeus Belived In The Fixity Of Species By Divine Creation And Died 31 Years Before Darwin Was Born. Why Then Does The Taxonomic System That Bears His Name Support Darwin's Theory Of Common

Carl Linnaeus Belived In The Fixity Of Species By Divine Creation And Died 31 Years Before Darwin Was Born. Why Then Does The Taxonomic System That Bears His Name Support Darwin's Theory Of Common — Preceding unsigned comment added by PAOH200 (talk • contribs) 13:47, 29 August 2012 (UTC)

Linnaean taxonomy is used in broadly to describe modern taxonomy in general, but in specific many aspects were dropped. For example, we no longer use Linnaean taxonomy for minerals. The basic observation made by Linnaeus is that species show a branching pattern of relationships, which is generally true in the case of plants and animals (but not absolutely so - see horizontal gene transfer). One way to account for this is that God willed it so, and indeed, the theory of evolution does not dispute that. What evolution does do is suggest a way in which it could have happened, which has since been borne out by a great number of experiments.

To make an analogy, when you find a brick lying in your living room, you might initially hypothesize that your son carried it in while he was playing. But when you find broken glass on the floor and a hole in your window, the brick is now evidence that someone threw a brick through your window. It is one of a set of observations that can be accounted for by a specific theory. Whether your son threw it in while he was playing ... bears further investigation. Wnt (talk) 14:07, 29 August 2012 (UTC)

Linnaeus didn't make that observation; he proposed an easy-to-use system of categorizing flora, fauna, and minerals so that naturalists in disparate parts of the world could sensibly known whether they were talking about the same critters or not, independent of whatever they were called in the local dialect. There is a fundamental issue regarding Linnaean taxonomy and Darwinian evolution, namely the species problem. But the trick there is that later, post-Darwin biologists have redefined their understanding of taxonomy into something quite different from Linnaeus (e.g. cladistics). The work of taxonomy today is somewhat related to Linnaeus, but the interpretation of what the taxonomy means varies starkly from those who see it as a series of fixed species, obviously. --Mr.98 (talk) 15:14, 29 August 2012 (UTC)

Darwinism is true, and the Linnean system is coherent with the facts. It doesn't intentionally support as in "argue for" Darwinism.. rather, the truth coheres. μηδείς (talk) 01:27, 30 August 2012 (UTC)

To take a simple analogy, Mendeleev produced the first Periodic Table of the Elements significantly before the development of atomic theory in its modern form, and yet the periodicity of the elements provides a good approximate understanding of the effects of subatomic structure on the physical and chemical properties of the element. In both cases, the classification system was not developed to promote the theory; the classification and the theory both describe the same scientific domain, and so used properly, they support each other. AlexTiefling (talk) 11:57, 30 August 2012 (UTC)

Though the table of Mendeleev was supposed to reflect actual natural categories, whereas Linnaeus' original work is meant more to be functional than natural (the sexual system for categorizing plants — by number of stamen, a rather arbitrary decision — is the most blatant reflection of this.) Linnaeus himself was actually somewhat explicit about this in the short first—1735— edition, if I recall. (It's actually quite a funny little pamphlet, if you can find a good translation... if only we naturalists could figure out whether we were all talking about the same bugs, he more or less says, then we could figure out ways to get rid of all these damned bugs. How insects in particular vexed him with their many ways of annoying humankind...) --Mr.98 (talk) 01:42, 1 September 2012 (UTC)

How audible would it be to a human?

These days, Charles Bolden and Will.i.am are amusing themselves by making their voices come out of a speaker on Curiosity on Mars. But Mars' atmosphere is very thin. I haven't been able to find out what the speaker's volume settings are, but if they are about strong enough such that on Earth, the volume would be 60 dB, about as loud as conversation in restaurant, office, background music, Air conditioning unit at 100 ft (source) at 3m distance from it, how loud in dB would it be about 3m away from Curiosity on the surface of Mars to a human who miraculously could survive without a helmet on? 20.137.18.53 (talk) 14:38, 29 August 2012 (UTC)

There is no speaker on Curiosity. The song and speech were transmitted back to Earth, not played on Mars. Bazza (talk) 15:35, 29 August 2012 (UTC)

Oh, after watching a video, I see that all that really happened was an audio recording was carried in a file on Curiosity, which beamed the electronic signal back to Earth. So we've been getting visual data from Mars since the 70s, but this is the first time we get audio from the surface. My POV, but that's kind of lame, and makes this headline seem misleading to me. 20.137.18.53 (talk) 15:42, 29 August 2012 (UTC)

If you watch the August 28 news conference, you'll see that at least two reporters were confused about what exactly this stunt was supposed to demonstrate. The answer was that this is the first rover with enough communication bandwidth to do this without interfering with more important data. Not exactly a significant milestone. --99.227.95.108 (talk) 20:09, 29 August 2012 (UTC)

Who gets paid for these sorts of publicity stunts? Wnt (talk) 20:44, 29 August 2012 (UTC)

It's still a viable question, though. All of a sudden the OP doesn't care to know?165.212.189.187 (talk) 15:12, 30 August 2012 (UTC)

Does 'Curiosity' have a microphone on board? if not, then why not?

Hi,

Does the Mars Rover 'Curiosity' have a microphone on board? If not why wasn't it planned for since I vaguely remember some scientists(Perhaps Carl Sagan) hoping to put a microphone on a Mars probe to hear the sounds of the Martian winds? — Preceding unsigned comment added by Gulielmus estavius (talk • contribs) 17:05, 29 August 2012 (UTC)

No. The scientific return is not high enough to justify the extra weight. [2]--Aspro (talk) 17:22, 29 August 2012 (UTC)

Aspro's link actually doesn't say why there wasn't a microphone, just that there wasn't. Plenty of people have pushed for including a microphone on a Mars mission, most notably the Planetary Society, whose microphone actually flew on the failed Mars Polar Lander. The Phoenix lander also included a microphone, but only because its descent imager (MARDI) happened to have a microphone on its circuit board. MARDI was turned off because it had a risk of interfering with IMU measurements during landing, which could have been fatal to the spacecraft. According to an interview I heard with a Planetary Society member (Emily Lakdawalla), the Society lobbied to have their microphone included on Curiosity, but it was rejected because the rover was already complex enough (she didn't elaborate on this, and I haven't been able to find a more detailed explanation). Personally I think that's a strange reason, because a microphone is one of the smallest and simplest electronic devices possible (just look at your cellphone to see how small it could be). Having one would be great for PR, and NASA only gets funding if the public is excited and inspired by its missions. --99.227.95.108 (talk) 22:26, 29 August 2012 (UTC)

You don't just need the microphone, though. You need a microprocessor, etc., to control it. The whole thing needs to be connected to the rover's power systems, and communication systems. Everything needs to be tested to make sure it doesn't interfere with anything else. Time needs to be scheduled to transmit instructions and results. Someone needs to control it. Someone needs to analyse the data. There is a lot involved with adding one seemingly very simple extra experiment to a probe. --Tango (talk) 22:36, 29 August 2012 (UTC)

I think we know what the sound of tires grinding along bare soil sounds like. I'm not sure there's a lot of scientific data to be gathered by putting a microphone on it. It's not like there are little green men who need a karaoke machine or something. --Jayron32 22:35, 29 August 2012 (UTC)

One reason might be that sound doesn't propagate well on Mars [3]: it's apparently a very quiet place. Not that you'd really expect to hear anything but wind and machine sounds from the rover anyway, but it would be easy from the LGMs to sneak up on you if you weren't paying attention: you'd never hear them coming (and their voices would be deepened by the carbon dioxide, sort of the opposite of the effect helium has). Acroterion (talk) 14:46, 30 August 2012 (UTC)

Certainly it would be worth hearing what Mars has to say, even if it is only the sound of its wind, of blowing grains of dust, the crunching of soil beneath the tires, maybe the occasional strange drummings of settling sand dunes. Sound carries a long way and it carries a lot of information. Maybe once in the mission it would even be something spectacular, a landslide on an old weathered slope that the surveyor can then locate from orbit.

The problem of the thin atmosphere and CO2 absorbing sound, of course, is serious, and it may be very difficult to get a sufficiently sensitive microphone to Mars. But apparently the CO2 absorbs mostly high-frequency sound, over 2000 Hz [asadl.org/jasa/resource/1/jasman/v10/i2/p89_s1], and absorption is affected by impurities like water vapor [4] (though I haven't read to see how). I wouldn't dismiss the idea so quickly - seeing another planet gives us a feeling for what it is, but hearing it gives us a sense of the spirit of the place. Wnt (talk) 15:00, 30 August 2012 (UTC)

InSight will have a seismometer so we may be able to hear what Mars has to say soon, at least in the seismic domain. Sean.hoyland - talk 16:08, 30 August 2012 (UTC)

I don't disagree: there are few places that we can get to that would provide an opportunity to listen to alien winds, and it would be extremely cool. Acroterion (talk) 17:54, 30 August 2012 (UTC)

Certainly it would have been cooler to hear some Martian winds than a rather ordinary Wil.I.Am single. Gulielmus estavius (talk) 18:03, 30 August 2012 (UTC)

What is ordinary Wil? (Sorry to hear you are single.) μηδείς (talk) 23:33, 1 September 2012 (UTC)

Someone asked this question during an "Ask Me Anything" session on reddit with the Mars Rover engineers this was their response:

We took a microphone on the Phoenix Mars Lander, and we turned it on but essentially heard nothing (white noise) so it was never released. We don't really need it for any experiments.

We do have the landing signal sound as it sounded from one of the orbiters.

-Keri/@KeriOnMars

Here's a little more info on the Phoenix microphone. It was essentially a hitch-hiker. It was built into another instrument taken off the shelf for the the lander, but it was never intended for the mission. There was no science team or budget connected to it. Since it was not intended for use it was never tested before launch and never entered into the power budget for the lander. Only after Phoenix successfully completed it's mission, 5 months after landing in the polar region, was the mission somewhat willing to test it. They couldn't do it earlier because they couldn't risk the prime goals of the mission if anything went wrong. The project manager was fairly certain it wouldn't work and was against trying it because he didn't want to raise expectations. His mind changed when we got a tweet to the @MarsPhoenix account from a man who said he was blind and how much he wished he could hear Mars because he couldn't see the pictures. A couple days later, they sent the signal to Phoenix to turn it on but we got.. well.. nothing. Empty files. If we had received anything, it would have been released. The team figured the mic was frozen solid and decided to give it a second try by leaving it on longer to warm up. Unfortunately, the Phoenix mission lost its last bit of power (as expected) before it got the second instruction. -vm

-- MacAddct1984 ^{(talk • contribs)} 17:08, 2 September 2012 (UTC)

I get the advantages of sexual reproduction, but what are the advantages of having separate sexes?

I read this article which suggests lesbians could create one day create sperm from their own bone marrow cells so they would be able to have children. However, I intuit that they would only be able to produce girls. If those girls were lesbians too, I could see a self-sustaining "Amazon" type of society, without the need for men. Which makes me think, why did mammals evolve separate sexes anyway? Couldn't you have meiosis without the need for separate sexes? After all, many plants have male and female gametophytes coming from the same plant/sporophyte. It seems to me you could have twice the reproductive capacity without the need for "dedicated" males.

I understand the selfish gene argument for why the sex ratios are 1:1, but that doesn't explain how the separate sexes got created. What was the evolutionary incentive for initiating separate-sex "sporophytes"? If selfish genes could create one parasitic class which cannot directly reproduce, why didn't they end up creating many? 71.207.151.227 (talk) 17:12, 29 August 2012 (UTC)

You are asking about evolution of mating types. That article is woefully stubby, but it does mention one use, which is regulation of reproduction. Many plants go to extremes to reduce the possibility of self-pollination, because having sex with oneself takes away many of the advantages of sexual reproduction in the first place. Some fungi take multiple mating types to the extreme, and have many thousands of sexes. Other plants are happy to self, but that's a different story. In fact, many different mating systems have developed, based upon the challenges that an organism faces, which depend on its life history, habitat, etc. Many species do exist mainly as hermaphrodites, such as many slugs. Note that separate mating types don't necessarily imply polymorphism (or sexual dimorphism). That starts with anisogamy, which arose long before mammals appeared. I'm not sure, but I think all chordates animals employ anisogomy, even in the case of hermaphrodtic slugs. The other case, isogamy (but still with different mating types) is apparently restricted to algae, fungi, and a few other groups. Finally, some unusual species are confined to one sex, such as the bdelloid rotifers. But that's not really true sexual reproduction, more of some weird derived intermediate state between sexual and asexual reproduction. SemanticMantis (talk) 18:45, 29 August 2012 (UTC)

As soon as there is some sort of heritable variability in sex cells, the "male" strategy of small and motile will become hugely successful compared to medium sized and immobile, since "sperm" will be much cheaper to produce in quantity and more likely to "score" than medium sized sex cells. Once sperm become ubiquitous, the rare egg will become a much more valuable commodity, and its increased size will increase viability, while its selectiveness among sperm (sexual selection) will increase the quality of offspring produced. First the male strategy is highly successful, and then presence of males makes the female strategy itself successful, leading two two stable "solutions" to the sex problem. μηδείς (talk) 01:24, 30 August 2012 (UTC)

Sexual reproduction is actually a very difficult topic, and I don't claim to know all the relevant philosophy. But the basic point is that when you have different mating types, they tend to be nearly evenly distributed (with intriguing exceptions) because it is advantageous to join an underrepresented sex to produce more offspring. And although my intuition would suppose that penis fencing is in all regards the most advanced sexual condition, it would appear that in reality most species find that putting all the effort either into being male or being female delivers more reward than splitting it up. Wnt (talk) 06:24, 2 September 2012 (UTC)

Telomeric fusion and human evolution

It is well known that human chromosone 2 is just a fused version of primate chromosomes. But I have problems understanding how the new lineage that would eventually lead to modern humans actually propagated. If one individual had the chromosomal mutation, how could he even mate if the surrounding population had a different number of chromosomes? Or is it more likely that more than one individual had the same random chromosomal mutation? --Ghostexorcist (talk) 17:34, 29 August 2012 (UTC)

Having different chromosome numbers is not necessarily an impediment to reproducing. The various subspecies of horses have different chromosome numbers, and can still mate and produce fertile offspring. thx1138 (talk) 17:57, 29 August 2012 (UTC)

Can you give specific examples? I know mules are born sterile because they get an uneven number of chromosomes from their horse and donkey parents. A geneticist suggested several years ago that the lineages that eventually gave rise to modern humans and chimps might have continued to breed after their initial split and later split for a second and final time. Just like female mules can sometimes breed, the female hybrids could produce viable offspring. I don't think this has ever been proven, though. If the populations with different chromosomes could breed, I guess drift would play a part in making the fused chromosomes a dominant trait. --Ghostexorcist (talk) 18:15, 29 August 2012 (UTC)

Note that horse and donkey have some differences in the overall chromosome structure as well as the number - it's not as simple as the end-to-end fusion in humans.[5] Wnt (talk) 21:28, 29 August 2012 (UTC)

Stages of meiosis

It basically comes down to a question of whether meiosis can still occur, or whether it gets blocked at some stage. Looie496 (talk) 18:37, 29 August 2012 (UTC)

Note there are genes at the fusion site of substantial interest. As for the genetics of it, the 1-2 would still be homologous to 1 and 2; the only question is whether sometimes the 1-2 gets pulled between opposite poles and torn apart (embryos which would be weeded at an early stage). I haven't figured that one out, but there's at least a 50-50 chance it wouldn't happen, simply by chance. Wnt (talk) 21:16, 29 August 2012 (UTC)

These explanations are helpful, but does anyone know of a particular book or paper that describes the process in full? --Ghostexorcist (talk) 22:34, 29 August 2012 (UTC)

I don't think it is really understood. As far as I can see, the most informative paper is this one, for what it's worth. Looie496 (talk) 23:15, 29 August 2012 (UTC)

Thanks. Carl Zimmer pointed me towards this paper. I figure others interested in the subject might want to check it out. --Ghostexorcist (talk) 21:32, 31 August 2012 (UTC)

Any acquired immunity to rubella when an infant gets it pre-vaccination?

According to Rubella, the first administration of the MMR vaccine usually occurs around 12-18 months, but I wonder if a baby experiences the virus before that vaccination, does the baby's immune system get any "education" on how to combat future exposures from that? I'm not talking about CRS or an extremely young newborn, and of course this is not to say that that would preclude vaccination (that's not even my question). I was just wondering the biological question of whether or not an as-yet non-vaccinated human gets any immunological benefit after having gone through it and survived it in the specific case of Rubella. 20.137.18.53 (talk) 20:29, 29 August 2012 (UTC)

Rubella being more commonly known in the UK as "German measles" when I was growing up, the received wisdom was that you could get it more than once. I myself had it three times before I was 20. Measles, however, you only got once, and I can remember going to measles parties so that I'd get it and be immune. Vaccinations for these diseases didn't exist when I was a little girl. (This was, of course, in the dark ages BC - Before Computers.) This is, of course, completely OR and unsourced and I'd appreciate it if someone could provide some proper references. --TammyMoet (talk) 20:35, 29 August 2012 (UTC)

It is sourced, we're just not "reliable". ;) 21:59, 29 August 2012 (UTC) — Preceding unsigned comment added by Medeis (talk • contribs)

This appears to say that you only get rubella once.[6] Rmhermen (talk) 22:56, 29 August 2012 (UTC)

I always wondered what actually happened at measles parties; do you go around kissing each other? (The article doesn't say.)--Shantavira|^{feed me} 10:21, 30 August 2012 (UTC)

We basically sat and played games together as far as we could, and kissed bye-bye... --TammyMoet (talk) 14:02, 30 August 2012 (UTC)