Wikipedia:Reference desk/Archives/Science/2009 April 24

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April 24

Blowing bubbles

Why do the children's toys that you dip into soapy water to blow bubbles with have all those vanes on them? How is this design better than just a plain plastic loop? Dismas|^(talk) 00:04, 24 April 2009 (UTC)

More surface area? --140.247.10.147 (talk) 00:21, 24 April 2009 (UTC)

The vanes (those grooves along the edge is what I assume you are refering to) hold extra soap, which is fed into the bubble blowing area after you blow a bubble. With a plain plastic hoop, you'd only get one or two bubbles before having to reload; the vanes allow for more bubbles to be blown on a single dip. As a father of a three-year old, I have must first-hand knowledge in this field of study... --Jayron32.talk.contribs 00:39, 24 April 2009 (UTC)

I was referring to the grooves. Thanks! Dismas|^(talk) 16:58, 24 April 2009 (UTC)

Function of globose

Dear Wikipedians:

The globose nucleus of the interposed nuclei of the deep nuclei portion of cerebellum: does it function to reach or grasp an object?

Thanks,

65.95.97.109 (talk) 01:29, 24 April 2009 (UTC)

I couldn't find any information specifically about the function of the globose nucleus. From "Color Atlas of Neuroscience", Greenstein, p. 202: "The spinocerebellum exerts control over axial musculature through the efferent outputs from the vermian cortex and the fastigial nucleus. It controls limb movements through outputs to the globose and emboliform nuclei." Other texts provide similar information. Axl ¤ [Talk] 08:40, 25 April 2009 (UTC)

Water consumption while dehydrated

From the dehydration article: "It is wise to slowly drink liquids when dehydrated." I've heard that advice all my life but never really understood why. Also, how come most poisonous product labels advise: "if ingested, do not induce vomiting." I figure vomiting would be a good idea and all if you just swallowed something poisonous? TravisAF (talk) 02:41, 24 April 2009 (UTC)

Once someone starts re-hydrating, the risk is in rapid fluid shifts (since the dehydration won't get any worse). So there's generally no rush to the re-hydration, but overdoing it can cause electrolyte imbalances. Regarding your second question, it's a bad idea to induce vomiting for caustic substances like drain cleaners, because they can cause significant damage on the way up - better to let a poison control center advise on how to treat. --Scray (talk) 03:05, 24 April 2009 (UTC)

Another concern about induced vomiting is the risk of aspiration of vomitus into the lungs. Some toxins will be absorbed much more rapidly from the lungs than they would from the stomach, other nasties – like the caustics Scray mentions – are apt to do much more severe damage to the delicate tissues of the lung (compared to the relatively tough lining of the stomach). Inflammation of the lungs or trachea (caused by even small amounts of aspirated vomitus) may close airways and make a bad situation much worse. TenOfAllTrades(talk) 03:30, 24 April 2009 (UTC)

For more on the electrolyte-imbalance thing, see water intoxication. It can kill. --Anonymous, 03:59 UTC, April 24, 2009.

Indeed, if you are drinking water, rather than specially designed re-hydration fluids, you could get into serious trouble. Anything more than very mild dehydration should be treated with proper salts, not plain water. (Rule of thumb: If you can drink the re-hydration stuff without it being so disgusting it makes you gag, then you need it.) --Tango (talk) 10:30, 24 April 2009 (UTC)

It might be worth pointing out that "dehydration" goes way beyond just being thirsty. I've frequently come back from a desert hike or bike ride and slugged down a half gallon of water or Gatorade without ill effect. You have to be gallons down before you get into really serious concerns about rehydrating in the right way. Looie496 (talk) 19:00, 24 April 2009 (UTC)

Indeed, half a gallon wouldn't generally be enough to cause a problem. I think not eating properly can increase the risk - it's all about the balance between water and salt, if you aren't getting enough salt in your diet (NB: the required amount of salt is very low - this is not an excuse to put loads of salt on your chips!), even a small amount of water could be too much. When you've been on these hikes, etc., you have probably been eating high energy food like chocolate - the milk chocolate wrapper I've just looked at says it has 200mg of sodium per 100g, the RDA (according to Wikipedia) being about 1500mg, this is a good example of how much salt there is in many of the foods we eat. --Tango (talk) 19:56, 24 April 2009 (UTC)

Lost in the woods

If i became lost in the woods, why would i not just eat grass and leaves until i found my way? It seems obvious to me to eat them if i was starving. EVAUNIT-666 03:38, 24 April 2009 (UTC)

Watch out for leaves of three etc. :-) By the way, do you have a Science question? --Scray (talk) 03:49, 24 April 2009 (UTC)

The question is why you can't survive on grass and any old leaves: after all, some animals are happy with that sort of diet (and there are some leaves we do eat, such as lettuce). The main difference is that humans can't digest cellulose, which tends to be a large constituent of various kinds of plant material. Also, some leaves may be toxic, as Scray points out. However, we do have a long list of plants with edible leaves, with some cautions at the top. --Anonymous, 04:04 UTC, April 24, 2009.

You won't be able to get much nutrition from grass as was explained above. Dehydration should be bigger concern anyways. Dauto (talk) 04:29, 24 April 2009 (UTC)

Are you a cow or other ruminant? Edison (talk) 05:20, 24 April 2009 (UTC)

If you get lost in the woods, you may want to remember that an average adult should survive some hours without shelter, some days without water, and some weeks without food. (YMMV: weather and your starting physical condition will greatly affect these estimates. If you are in the snow or in the desert, adjust accordingly.) "OMG! I NEED TO EAT RIGHT NOW!!!" should not be your first concern, even when you start to feel a bit peckish. First worry about sleeping out of rain, wind, hot sunlight, and night frost. Later think about clean water. 88.114.222.252 (talk) 12:44, 24 April 2009 (UTC)

There we go again. What's up with that? That's the second time I see someone on these pages talking about people not being able to survive more than a few hours without shelter. That's only true on the most extreme conditions. I would worry first about water if I got lost in a forest. Dauto (talk) 17:44, 24 April 2009 (UTC)

What woods, when and where? As noted above the human digestive system is ill adapted to gain much nutrition from grass. However, most forests will provide nuts and berries which you could very well live on for a while. You'd have to know what grows where and when locally. Many plant buds and some flowers are also edible and contain more energy than leaves. The problem would also be that gathering all those would be taking time you might spend better on finding the next road or river. (Most flowing water ends up at/near human habitation downstream sooner or later.) 76.97.245.5 (talk) 15:55, 24 April 2009 (UTC)

If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --131.188.3.21 (talk) 13:32, 26 April 2009 (UTC)

That works even in the rainforest. In a flat, boggy area it might be more difficult. 76.97.245.5 (talk) 01:26, 27 April 2009 (UTC)

SALTWATER FISHES

Can fishes striving in salt water also survive in fresh water? —Preceding unsigned comment added by G4J (talk • contribs) 04:40, 24 April 2009 (UTC)

see fish migration, they would be termed diadromous fishes, more specifically anadromous or amphidromous.—eric 04:55, 24 April 2009 (UTC)

To clarify, most fish can only survive in one environment or the other, but there are some, such as salmon, which can handle either fresh- or salt-water. StuRat (talk) 07:38, 24 April 2009 (UTC)

Take a look at osmoregulation to see why it's difficult for fish to move between the two. Smartse (talk) 15:19, 24 April 2009 (UTC)

the earth

what is the exact circumference of the earth ,(polar and equatorial both. —Preceding unsigned comment added by Khan iqbal akhtar (talk • contribs) 05:24, 24 April 2009 (UTC)

From the top of the Earth page... 40,075.02 km (equatorial)

40,007.86 km (meridional) 40,041.47 km (mean) TravisAF (talk) 05:38, 24 April 2009 (UTC)

"exact" is a tough thing here...the earth isn't a billiard ballapparently, it is...see below! But the numbers from the Earth article that TravisAF quotes above are pretty reasonable. The standard for the shape of the earth that is most commonly used in exacting applications is called 'WGS-84' or World Geodetic System from the World Geophysical Survey of 1984. The values it gives are the best "mean sea level" description of the shape available - and I presume that the numbers above are from that definition. However, if you stretched a piece of string around the circumpherence of the planet then measured it - the answer would not be exactly that given above - and the result would vary depending on where you measured it - and probably on where the sun and moon were at the time because shape of the earth is affected by tides. It's probably also worth mentioning that the surface of the earth is like a fractal - so a precise measurement even at a particular moment in time and a particular direction over the planet is going to suffer from the Coastline paradox (see also: How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension).

SteveBaker (talk) 13:24, 24 April 2009 (UTC)

"The earth isn't a billiard ball". From the above figures the earth's circumference varies by only a few parts in a thousand. Are billiard balls that accurately spherical? And the bumps in the earth are less than one part in a thousand. Are billiard balls smoother than that? DJ Clayworth (talk) 15:09, 24 April 2009 (UTC)

From Earth: "Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls." Dragons flight (talk) 15:16, 24 April 2009 (UTC)

Wow! That's a cool observation. But - an 0.17% tolerance means that when we say the circumpherence is 40,041.47 km - we're overstating the precision by a couple of orders of magnitude! SteveBaker (talk) 19:39, 24 April 2009 (UTC)

Of course, the number is almost exactly 40,000 kilometers because that was the original definition of the kilometer; it was defined as 1/10000 the distance between the north pole and the equator along a meridian of longitude; which would be 1/4th of a circumference. But you all knew that... --Jayron32.talk.contribs 21:27, 24 April 2009 (UTC)

This reminds me of a study that I think appeared in the Journal of Irreproducible Results, where the authors tried to determine whether Nebraska (or maybe it was Kansas?) was indeed "as flat as a pancake". The conclusion was that it was very much flatter than a pancake. If it were only as flat as a pancake, there would be miles-deep canyons all over the place. Or something like that. --Trovatore (talk) 21:32, 24 April 2009 (UTC)

It was the Annals of Improbable Research, here. Algebraist 21:39, 24 April 2009 (UTC)

The above discussion correctly notes that the Earth is smoother than a billiard ball, but it's not quite round enough. Discussion here. --Sean 22:46, 24 April 2009 (UTC)

Yes - the poles are considerably squashed compared to the equator. The problem here is that we're presented with numbers that are accurate to 10 meters! Even with (proportionately) billiard-ball smoothness - that's way too much precision. Having just one mountain or valley along your chosen "circle" will throw off your measurement of the circumpherence by vastly more than 10 meters! That number can only be the result of a specification for the idealised shape of the earth - per WGS-84's ruling on the matter. SteveBaker (talk) 00:06, 25 April 2009 (UTC)

Or simply an average. --Tango (talk) 00:26, 25 April 2009 (UTC)

Smoothness and roundness are similar. The way I think about it is as a "power spectrum". Using a spherical harmonic breakdown (such as the set of WGS-84 coefficients), you can actually see how much "energy" is contained at each "frequency" (really, it's not energy, because it's a geometric description, but "frequency" is a moderately reasonable word - the spherical harmonics functions map well as spatial frequencies, albeit not sinusoidal frequency). And I'm sure you could find some way to represent mass-distribution as gravitational potential energy too, so "energy spectrum" is not really such a bad terminology after all). Anyway, the point is, Earth's deviation from perfect sphere is evident at the lower-order terms of the spherical harmonic decomposition, and its roughness is evident from the magnitudes of the higher-order terms. With sufficient number of terms, (impractical and unwieldy, but definitely possible), every topographic feature could also be described. The magnitudes of those coefficients would be REALLY small (in the same way that a band-limited radio-signal has zero spectral power at "infinitely high" frequencies). Nimur (talk) 14:47, 27 April 2009 (UTC)

Name

What's the name given to a situation when you hear something going on in a dream, then you wake up to hear it going on in the real world? 58.165.23.195 (talk) 07:14, 24 April 2009 (UTC)

You might be thinking of something paranormal, such as precognition or premonition. Or you might have fallen asleep with the television on.

Ben (talk) 07:36, 24 April 2009 (UTC)

Sounds more like he's asking about a real-world sound making it into a dream (very possible) and then waking up with the sound still there. Nothing paranormal about it. :) -- Aeluwas (talk) 08:49, 24 April 2009 (UTC)

According to our article, a commonly used term for this is "dream incorporation".--Rallette (talk) 12:15, 24 April 2009 (UTC)

The first link between protein and gene

Forgive me if I missed it, but I think I skimmed all the relevant pages on Wikipedia and didn't see anything. I've been wondering lately how the earliest links were drawn between proteins and genes. Many genetic mutations were connected to visible phenotypes long before the central dogma was developed. Was the connection with a particular protein made for any of these mutations? How were the chemical functions of the earliest studied proteins identified? Thank you. Someguy1221 (talk) 07:44, 24 April 2009 (UTC)

First, check out http://en.wikipedia.org/wiki/RNA_world

The current theory from my biology book is that RNA was a molecule which dabbled in several roles of the cell. It did things which we think of proteins doing--regulating the rates of reactions, and they were involved in metabolic pathways and they even stored "blueprints" for other RNA molecules (because remember, RNA can be transcribed off of another RNA strand--that is how RNA viruses do their thing, theey call it "the RNA directed synthesis of new RNA".

Also don't over hype the difference between RNA and DNA. The difference is only an oxygen on the sugar backbone. All that "difference" does is help the molecule be more stable. DNA can last several years, RNA can last only about 45 minutes on its own, without being sequestered from common reagent molecules.

The difference between RNA and protein, is well, that RNA is an acid. Both molecules owe their properties to organic chemistry. Both RNA (in the rna world) and current proteins had the same exact functional groups. However, proteins generally were more effecient, could fold better, and were recycleable.

In a way, your question could be answered that evolution took place and RNA simply became excinct because it is a fierce job market inside the cell, and well, RNA's job got sent overseas and only a few vestigial pathways still utilize RNA as a reactant in reactions today. Some even in your own cells!JameKelly (talk) 08:49, 24 April 2009 (UTC)

That answer seems a bit off topic to me... I certainly could be wrong, but the way I read the question, the OP is interested in the first example of a gene (i.e. the DNA sequence) being causally related to the protein it codes for. I think the answer you are looking for is found in the biochemistry article, which discusses the discovery and characterization of proteins. The first instance of a gene being linked to the enzyme it produces (from Biochemistry): "In 1958, George Beadle and Edward Tatum received the Nobel Prize for work in fungi showing that one gene produces one enzyme" (for research performed in the 1940's). The History of biochemistry article, which should be a good resource, is focused more on the 1800's and is surprisingly sparse on the advances of the 20th century. --- Medical geneticist (talk) 11:11, 24 April 2009 (UTC)

In addition (since the OP is interested in mutations & phenotypes) -- Archibald Garrod is widely acclaimed as the first to postulate that an inherited disorder could be due to deficiency of a particular enzyme, as in the case of alkaptonuria. However, although he made the connection in the early 1900's, the actual enzymatic deficiency was first demonstrated in 1958 and the gene mutations weren't described until 1996! In terms of the discovery of genetic mutations that cause disease, it's hard to ascribe a "first" for many things since many discoveries are made in parallel. There is a nice timeline at the National Human Genome Research Institute (http://www.genome.gov/25019887) that shows the progress from Beadle & Tatum's "one gene one enzyme" theory in 1941, the discovery of the double helix structure in 1953, discovery of the genetic code in the 1960's, development of DNA sequencing in the 1970's, to the first human disease gene Huntingtin being mapped in 1983 and cloned in 1993. Genes that are defective in chronic granulomatous disease, Duchenne muscular dystrophy, and retinoblastoma were all mapped and characterized in the 1980s-1990's, with many more following after that and still continuing today. --- Medical geneticist (talk) 13:12, 24 April 2009 (UTC)

Differential Capacitive sensors

Well i want to be very frank. I am a first year undergraduate Electrical Engg student. For joining one of my professors for a summer time project, he gave me a paper something to do with "Switched Capacitor Dual Slope Capacitance to Digital Converter For Differential Capacitive sensors". Unfortunately, being just a first year, i haven't the faintest inkling what these terms mean, except the term capacitor! I have tried searching on Google and wiki, but the sites only give highly technical information way above my head. However, i am determined to understand this topic. So can someone please explain me what the above mentioned terms are, in a down to earth, layman manner, so that a person with just basic electrical knowledge would catch the point ? Or perhaps suggest a link which does so? I am dearly in need of help !!Rkr1991 (talk) 10:13, 24 April 2009 (UTC)

Well, I'm no expert - but we can try to break up that turgid title into manageable bites:

• Switched capacitor -- OK so we're going to use a switch to choose one of two or more capacitors.
• Dual slope -- So the graph of some function is going to have two straight-line slopes. Probably because the slope changes when you switch from one capacitor to the other.

• No, its because the ADC counts up to the input and then down to a reference voltage. SpinningSpark 15:00, 24 April 2009 (UTC)

• Capacitance to Digital convertor -- sounds like an analog to digital convertor that measures capacitance instead of voltage.
• Differential Capacitive sensor -- well, whenever something is 'differential' you're either measuring the rate at which something changes or the difference between two things - this 'convertor' is clearly a 'sensor'.

So I guess (and I'm no expert either!) that this is a project to build a gizmo that measures some aspect of the capacitance of something using a computer. How it's gonna work is by somehow switching capacitors on and off. I think I'd start by searching on "Capacitance to Digital convertor" to understand how capacitance is measured digitally.

I agree that this does sound a little tough for a first year project - but that's the point of doing things like this with experts in the field. So talk to your professor. He's there to teach you - and if you don't understand what the heck this thing is - it's because (I presume) he has not yet taught you about it. That's his fault, not yours. So make every effort to read as much as you can - then go to him and ask for an explanation and a break-down of the project into bite-sized pieces.

Hopefully others here will be able to explain this in more detail.

SteveBaker (talk) 13:09, 24 April 2009 (UTC)

(ec) A dual-slope analog to digital converter (ADC) is a specific type of ADC commonly used in digital multimeters. It is described in our article integrating ADC which is an alternative name for it. It is more accurate than a single-slope ADC because it lets through a greater number of clock pulses but is slower to update as a result. The "switched capacitor" bit of the title is probably referring to changes of range, which are achieved sometimes by switching the value of the integrating capacitor and sometimes by switching the value of an offset voltage or current. The "for differential capacitive sensors" is probably referring to the type of input that is being measured. Many transducers (eg displacement detector) are essentially capacitors and the quantity being measured physically moves one of the plates causing the capacitance to change. The requirement of the measuring system is thus to measure the capacitance, either absolute, or the difference between the transducer and a reference capacitor (hence differential). Of course, some of that is guesswork; for a more specific answer you will need to provide a link to the paper you are reading, or at least some of the details (author, exact title, journal, date etc) and hope someone here has access to it. SpinningSpark 13:17, 24 April 2009 (UTC)

Learning something new requires juggling some number of unfamiliar concepts in short term memory. With time and effort, you can push concepts into your long term memory - once you have done that, you have "learned." When learning is difficult, that means you are encountering too many unfamiliar concepts at once to fit into your short term memory. This happens readily because short term memory is very limited - most people can only manipulate between four and seven "chunks" of information that way. Short term memory seems to work like a FIFO queue - if the unfamiliar chunks keep coming, they push earlier chunks out, and you lose them. Your emotional brain responds by generating emotions of anxiety and frustration. Long term memory, in contrast, is seemingly unlimited. As long as your brain continues to work, you can apparently just keep pushing more knowledge into your long term memory. The problem is that chunks can only move from short term memory into long term memory at a slow rate. Because short term memory is very limited, and long term memories can be slow to form, humans hit on a trick, thousands of years ago, to augment memory: writing. When you are trying to learn something that overwhelms your short term memory, you should immediately start writing. For example, read the paper you are trying to understand, but don't worry about understanding it right away. Instead, do this:

• Make a list of all the terms in the paper you don't understand yet.
• For each term, try searching the Web and so on, and write whatever you find that might relate to it.
• Keep coming back each day, re-read the paper, review your list of terms, and see if you notice anything you missed before.
• Look up all the references that the paper cites, read them, and see if any of them shed further light on your list of terms.
• Identify your conceptual sticking points. You will figure out some terms sooner than others. When you figure something out, move it to the bottom of your notes. Keep the unknown items at the top.
• Look for clues about the interrelatedness of terms. Probably every jargon term in the paper relates to the other jargon terms in various ways. The paper is not just a stream of consciousness list of random terms. You want to understand not only what each term means in isolation, but why the author used them all together. Sometimes you can understand the relationship between two items before you fully understand the items. See: ontology.
• Show your notes to some experts, and ask them to comment. They may suggest introductory references you can read, or they may point out errors in your thinking. For example, you might have listed a particular concept more than once, because maybe the paper refers to it by synonyms. In that case, your problem got simpler, because instead of two concepts to learn, you find you only have to learn one.

--Teratornis (talk) 22:34, 24 April 2009 (UTC)

I couldn't find the exact link on the net, but here are its details :
Novel Switched-Capacitor Dual Slope Capacitance to Digital Converter for Differential Capacitive Sensors
by, Boby George, Member, IEEE and V Jagadeesh Kumar, member, IEEE. I hope someone would be able to find the exact paper, and then explain what exactly is the problem being approached, and the principle used in this case.
I would like to add that it is not my professor's fault for not teaching this. I, being free in the coming summer, approached him for doing some extra work, and he has offered to take me in his research team as an assistant, if i can tell him what i understood from this.(He is one of the authors of this paper.) Thanks in advance for all the help.Rkr1991 (talk) 06:33, 25 April 2009 (UTC)
I would also like to thank 2 particular users - SpinningSpark and SteveBaker, who have both helped me out on numerous questions. Thanks for your time guys ! And thanks to Teratornis too...Rkr1991 (talk) 07:13, 25 April 2009 (UTC)

No, I can't find it either, but I did find this and wonder if the paper you have is a pre-print of the published paper with a different title. Sorry, I don't have a current subscription to IEEE Explore so cannot read it, and it doesn't have an abstract. You might want to take a look at this book though, which you can preview in google books. SpinningSpark 12:38, 25 April 2009 (UTC)

I can get a link of that paper... but i think these two papers were similar, but not the same.., so here goes.. http://measurements.iitm.ac.in/Publications/Papers/Journals/IEE-CDS.pdf Rkr1991 (talk) 16:36, 25 April 2009 (UTC)

Eggplant

does the eggplant causes hair loss? or this is a myth?? Maen. K. A. (talk) 11:46, 24 April 2009 (UTC)

Eggplant is in the nightshade family which contains toxic substances. Hair loss may be an effect of poisoning from ingesting unripe/inedible parts of the plant or an allergic reaction. As our article notes aubergines are high in nicotine, which can cause hair loss through constriction of blood flow to the follicles and accelerated cell aging. That is for prolonged exposure and high quantities, though. I doubt the average person would regularly eat 9 kgs of eggplants. That would signify a highly deficient diet that would cause many other health effects. High doses of caffeine can also cause hair loss, while low doses actually stimulate hair growth. This page [[1]] recommends eggplant leaves as a remedy for hair loss, but I'd rate that one under "people will try anything". 76.97.245.5 (talk) 15:14, 24 April 2009 (UTC)

"Female" DNA

Google doesn't lie ... so there is "male DNA" and "female DNA" (the question for "male Cellulose" and "female proteins" (the shapely ones) comes later...). Question: When "female DNA" is found at a crime scene, does that mean that no Y-chromosome genes were found in this sample or was there another test done ? (because X-Chromosomes are found in males and females). Does "The blood in the car showed female DNA" actually mean "in the blood we found no Y-chromosome genes but lots of other genes and human markers, so it must be the blood of a woman/female" ? Thanks --83.141.221.231 (talk) 14:38, 24 April 2009 (UTC)

I don't know the answer but most likely the absence of Y specific markers would indicate "female". Of course if the woman had AIS then the test would be misleading. And any test that relies on the absence of a marker is prone to contamination from other sources. David D. (Talk) 14:42, 24 April 2009 (UTC)

Another possible way to confirm a "female" sample would to look at a lot of polymorphic markers on the X chromosome. A male would have only one in every case (hemizygous for X) but a female would be heterozygous for many of the markers. David D. (Talk) 14:48, 24 April 2009 (UTC)

What would you see in the latter case? Female: More bands than usual (male)? Could you conclude from the complexity of the pattern whether the blood was from 1, 2, more women? In the meantime, I found the (a) (SRY-F + SRY-R) and (b) (PABX-F + PABX-R) Primer-pair approach. A male should give 2 bands, a female one band, a mix (of blood) of 2 females should give 2 diff. (PABX-F + PABX-R) results. --83.141.221.231 (talk) 15:06, 24 April 2009 (UTC)

Could you also look at methylation status of the X chromosomes? Aren't one-half of the genes in the X-X system silenced? Franamax (talk) 17:04, 25 April 2009 (UTC)

You could not detect such a difference with PCR. It could be done using antibody pulldown, probably directed at lysine methylation on histones. In males the X sequences would far less represented than in females. But to be pedantic, what if a male had Kleinfelter's Syndrome (XXY)? Such a male would have half his X sequences silenced. And besides, the sensitivity would be problematic at a forensic level. David D. (Talk) 00:58, 26 April 2009 (UTC)

You're all overthinking this. "We found female DNA" = "We did a karyotype and the sex chromosomes were 'XX"". "We found male DNA" = "We did a karyotype and the sex chromosomes were "XY". Depending on the circumstances, it may not even be as complicated as that....e.g. we found male DNA in the sperm specimen. - Nunh-huh 01:12, 26 April 2009 (UTC)

Looks like you can differentially label the X and Y, so don't need a full karyotype.[2] That would also solve rare genetic combinations and multiple contributors, since it seems to allow counting of the chromosomes in whole cells. In other ideas, there are non-genetic ways to identify the sex of a biological sample, so "high levels of PSA" would mean the sample's DNA is probably male (though surprising-to-me high rate of false-positive), whereas DNA from a sample that also has high levels of various pregnancy horomones is from a female. Going the other way, if the biological sample is sperm, I can guarantee it contains DNA from a male. DMacks (talk) 07:24, 26 April 2009 (UTC)

Canis lilliputia and canis brobdingnag

What happens when a female St. Bernard/Wolfhound/Great Dane is impregnated by a male Chihuahua/Yorkshire Terrier/Toy Poodle? And what happens in the reverse situation? I assume this never happens naturally but would have to be by insemination (please correct me if I'm wrong). I imagine a very smalle female dog would have more trouble than the reverse situation, but is such a pregnancy viable? Are there any examples of such dogs carrying to term? And for the reverse, I imagine this might either kill the tiny female or, as the pup grows too big, her body will reject through a miscarriage? Or does it work that a female can carry and the combination of genes still results in a very small dog despite the large male breed? I've always wondered about this.--70.19.69.27 (talk) 21:42, 24 April 2009 (UTC)

This was asked here fairly recently. You may want to look at that thread. Deor (talk) 23:02, 24 April 2009 (UTC)

Thank you for that link Deor. Extremely unsatisfying answers based on sheer speculation but that may be because the answers are simply unknown.--70.19.69.27 (talk) 03:37, 25 April 2009 (UTC)

Wasn't that what I said in the first post? :-P Nil Einne (talk) 14:53, 25 April 2009 (UTC)