Science desk
< July 1	<< Jun \| July \| Aug >>	July 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.

July 2

Are the chromosomes in human nucleus with different genes or the same?

Always I thought that DNA is found in the nucleus as one long chain of genes. But yesterday I red the book "the stuff of life - genetics" that if I understand correctly it explains that it's not one long chain of DNA but the 23 chromosomes (in humans) are 23 parts of the whole one DNA. Is it correct?--31.210.182.248 (talk) 00:29, 2 July 2018 (UTC)[reply]

Yes. --Jayron 32 04:47, 2 July 2018 (UTC)[reply]

See Human genome. It's a bit more complicated than that. It's 23 pairs of chromosomes for the nuclear DNA, plus separate mitochondrial DNA. Each of the 23 pairs is different from the others. To grossly oversimplify, within each pair, each gene is represented on both pairs, but for each gene the pairs may have different variants of the gene. -Arch dude (talk) 05:35, 2 July 2018 (UTC)[reply]

Eukaryotes like "eu" and me have one or more linear chromosomes. The number of chromosomes varies between species. As stated above, humans are diploid, and have 23 pairs of chromosomes, and therefore 46 total, in all the normal, nucleate somatic cells. (Human red blood cells lose their DNA while maturing.) Human gametes are haploid, having only a single set of chromosomes; two gametes fuse to make the diploid organism. Prokaryotes most commonly have a single circular chromosome, but there is variation. Many have plasmids floating around as well. As also mentioned, our mitochondria have their own DNA. Moreover, they have it in the form of…a single circular chromosome! This is a huge clue to their origins as bacteria that moved in to early eukaryote cells and struck up a partnership. The plastids found in plants similarly have their own DNA, because they originated the same way. There's all kinds of fascinating stuff you can learn from DNA. Another neat one is that humans have two fewer chromosomes than chimpanzees, our closest living relatives. What happened to the other two? In the lineage that lead to humans, they fused together to form human chromosome 2; we can tell because that chromosome has inside it remnants of structures from the pre-fusion chromosomes. --47.146.63.87 (talk) 07:11, 2 July 2018 (UTC)[reply]

Psychology of introverts who have given up with close friends and relationships

I come across many people in the world who seem to be introverts (like their solitary time and prefer doing things on their own because it’s easier). Often they also seem to not want close friends or relationships and instead opt to get their social needs nets in organised ways such as language classes or hobby groups. They are not interested in meeting new people. Isn’t this contradictory of an introvert who I thought prefers close friends? 82.132.186.29 (talk) 07:22, 2 July 2018 (UTC)[reply]

A language group or hobby group is quiet and orderly compared to a party. Dmcq (talk) 08:30, 2 July 2018 (UTC)[reply]

The concept of introversion (originally formulated by Carl Jung) has changed somewhat over time. Modern psychologists tend to use the term as it was conceptualized by Hans Eysenck. Quoting from out article on extraversion and introversion: Hans Eysenck described extraversion-introversion as the degree to which a person is outgoing and interactive with other people. ... Extraverts seek excitement and social activity in an effort to heighten their arousal level, whereas introverts tend to avoid social situations in an effort to keep such arousal to a minimum. Looie496 (talk) 13:12, 2 July 2018 (UTC)[reply]

Ideal Gas Problem

I have been trying to do this problem from my physical chemistry textbook. I think I understand what the apparatus looks like that they're describing. If I understand it correctly, then with the first pivot configuration, when 423.22 torr of CHF₃ is surrounding the bulb, it becomes buoyant enough to reach the balance point. This would be when the density of the CHF₃ is the same as the average density of the bulb. For the same pivot setting, we would expect that the unknown fluorocarbon would also balance at the same density. We can get an expression for the density of the CHF₃ at the given pressure using the relationship $p={\frac {\rho RT}{M}}$ and rearranging to $\rho ={\frac {pM}{RT}}$ . Now we don't actually know the value of T as it's not given. We could make a reasonable assumption that it's about 300K, or we can instead just set the expression for $\rho _{CHF_{3}}=\rho _{Unknown}$ . Now we can just multiply both sides by RT to get rid of what we don't know. Now, we know p_unknown, p_CHF3 and M_CHF3, we we can just solve for M_Unknown. I get ~102g/mol. Now if we go through the same procedure with the numbers given for the other pivot setting, we should be able to confirm the answer, but instead I get a much lower result for M_Unknown of 90.5g/mol. There's few issues here. One is that it's really weird to have a chemical formula in the form C_xH_yF_z where it has a half Dalton for a molecular weight. Fluorine, carbon and hydrogen are all fairly close to round numbers, so it seems unlikely that that answer is possible. Another is that the pressure values given for the second setting are a bit weird. The pressure needed to bring the unknown into balance was much lower than in the first experiment, but the pressure needed to bring the CHF₃ into balance was slightly higher. All things being equal, that points to a higher density of the CHF₃ and a lower density of the unknown. If all things are not equal, and the temperature changed drastically between experiments, then might account for the diversion in the pressures of the two gasses required, but it seems like a pretty large deviation. I've been going over this problem for some time and haven't managed to make any breakthroughs. I'm starting to wonder if I'm either tackling it completely wrong, or if the problem itself has an issue. 202.155.85.18 (talk) 10:03, 2 July 2018 (UTC) Edit: In case anyone else has been wreaking their brain trying to solve this, I found the answer in the solutions manual. It's essentially what DMacks said below. 202.155.85.18 (talk) 01:22, 3 July 2018 (UTC)[reply]

I think this is from a fairly advanced textbook (physical chemistry—mid/upper-level undergraduate?), so even if you have correctly solved it, you may have to think about "real-world" issues. I agree with your math for each of the two cases. So consider that the ideal gas laws are only approximate and these values are actual experimental data. I have no idea how "ideal" your gases are, but are the gas laws more reliable at higher or lower pressures? Given one has a "physically impossible/unsolveable" decimal-value, does that cast doubt on the reliability of that measurement and you should exclude that result? Or if you know one gives a suspicious result, does that mean the other is also suspicious (albeit not by direct appearance) and you should somehow average them? DMacks (talk) 10:33, 2 July 2018 (UTC)[reply]

You could be right that additional, practical issues need to be taken into account, but my feel from doing dozens of other problems in this text is that they directly ask for you to comment on practical issues when presenting these questions. Certainly, the point you make about whether the first result is only a plausible value by pure chance, and that it ought to be regarded with the same scepticism as the second is something I'd been mulling over too. As far as the significance of the figures is concerned, I should be able to calculate precise values for the molecular mass to the second or third decimal place, but whether or not it's reasonable to lend such weight to those decimal places in an experiment of this type is just guesswork. This particular problem is from the section on ideal gases (actually, the text insists on the terminology "perfect gas" because the author draws some technical distinction between a perfect gas and a merely ideal gas), and this section is followed by the section on real gases. For that reason, I'd assume that this problem is intended to be solvable with only the concepts taught in the ideal/perfect gas section. Then again, maybe the problem is trying to demonstrate the limits of the ideal gas law to whet our appetites for the real gas section. Who knows? To answer your question, the ideal gas law is valid in the limit of

p\rightarrow 0

so the lower pressure results should be closer to ideal behaviour. Anyhow, thanks for your answer and your confirmation of my math and strategy for solving the problem. Whether or not I've actually solved the problem, it's made me think long and hard about the issues behind it and at the end of the day that's what the problems are meant to do. 202.155.85.18 (talk) 00:57, 3 July 2018 (UTC)[reply]

There seems to be an issue there. As you mention, you need to increase pressure of the known calibration gas and decrease that of the unknown gas to retrieve equilibrium in the second setting compared to the first one, so it cannot be that gas densities are equal at equilibrium (even outside the ideal gas law, at a given temperature and composition, density always increases with pressure). I suspect the problem is wrong (though I cannot find any plausible typo to fix the values), or that there is more to the experiment's description that you or I understood (after all, why give you two settings of the beam, since one can already obtain a molar mass measurement?). Tigraan^{Click here to contact me} 17:36, 2 July 2018 (UTC)[reply]

I guess the typo could be something as simple as them mixing up the pressure values? I'm doing the same amount of head scratching over why they overspecified the problem by giving the results of two experiments, unless it is just to illustrate the level of imprecision. 202.155.85.18 (talk) 00:57, 3 July 2018 (UTC)[reply]

Pressure values are given to 5 significant figures, so that's a big pedagogy mistake from a chemistry textbook, if the measurement imprecision is about 20%. I did think of a typo in the pressure values, but could not find any permutation of values or digits that yields something similar in both cases from a cursory search. Tigraan^{Click here to contact me} 07:57, 3 July 2018 (UTC)[reply]

Astronomy: How does an object get in a Lagrange point?

For instance, if an asteroid crosses the path of a LP, what are (very roughly) the sort of conditions needed for it to get trapped? And if we drop an object at some place a LP will be at later, can it get picked up? (Maybe the article could have a short section about it?) 193.253.244.40 (talk) 17:58, 2 July 2018 (UTC)[reply]

Only L₄ and L₅ points are stable and therefore objects can only be trapped in these two points. Trapping generally occurs when the velocity of an object becomes sufficiently low with respect to one of those points. This usually happens due to perturbations by other orbiting bodies. However this condition is reversible - if other bodies can push an object into a Lagrangian point, they can also push it out of that point. Ruslik_Zero 18:39, 2 July 2018 (UTC)[reply]

Is ths a variation of Newton's First Law of Motion: A system of bodies either remains gravitationaly bound or continues to be unbound, unless acted upon by a gravitational force? The gravitational force is generated by a change in the collective mass of the system. Thus, the smallest number of bodies required to form or disrupt the smallest system of two bodies, is three. During formation or disruption, the third body is ejected, and can either be pre-existing or generated from the breakup of a single body. IMO. Plasmic Physics (talk) 06:31, 4 July 2018 (UTC)[reply]

No. Newton's First Law says only that an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force. It speaks only qualitatively, not quantitatively, about the force; it is a law of inertia that does not encompass his quantitative Law of Gravity nor by itself give solutions to 2- or 3-body Orbit stability problems. These may be solved by applying small perturbations, see Orbit#Orbital_perturbations.DroneB (talk) 09:46, 4 July 2018 (UTC)[reply]

I'm just saying that a body approaching a LP won't slow down of its own accord, it will need to exchange momentum at just the right moment and vector, with a another body besides the host. Plasmic Physics (talk) 19:51, 4 July 2018 (UTC)[reply]

A small slowly moving body approaching the L₄ or L₅ point will enter into an orbit around the point. This is the trapping mentioned by Ruslik_Zero. There is no sudden stopping exactly at the LP. The LPs exist in the combined gravitational field of two hosts. DroneB (talk) 10:08, 6 July 2018 (UTC)[reply]

The Lagrangian points are weird in that they simulate a two-body problem, i.e. a "gravity well" of sorts, albeit one surrounded by tadpole orbits. Even so, they aren't really a two-body problem; you have the asteroid or probe, the moon, and the planet - hypothetically, an object might be captured or released by putting energy into or out of the planet-moon system. I don't know if this actually allows for some very clever orbit to infiltrate or exfiltrate objects from the point without acceleration, though that is never the way the topic is presented. There is some data that might be gotten from this, but I haven't read it, or possibly understood from here, though its emphasis is different. Note that an object wandering outward will eventually escape from a tadpole orbit to a horseshoe orbit, i.e. go from orbiting L4 to orbiting both L4 and L5. Most bodies do make such transitions over time, but I don't know if these necessarily rely on outside forces from other planets (which are unusually relevant, since the object can be nearly on the far side of the sun from the planet and moon it is "orbiting"!) . Wnt (talk) 11:48, 5 July 2018 (UTC)[reply]

In the restricted three-body problem L₄ and L₅ are stable if a certain criterion is satisfied, which means that a small body trapped in such a point will remained trapped forever (even if the orbit is an ellipse). Ruslik_Zero 19:03, 7 July 2018 (UTC)[reply]

DNA analysis of siblings

Siblings have (approximately) half of their DNA in common. With the analysis that shows what countries your ancestors came from, do siblings have the same breakdown? Bubba73 ^{You talkin' to me?} 20:13, 2 July 2018 (UTC)[reply]

There can be a meaningful amount of variation, as a result of genetic recombination. Consider, as an arbitrary example, chromosome 1. Each child gets two copies of chromosome 1, one from the father and the other from the mother. The copy from the father is actually an amalgamation of the father's two versions of chromosome 1, obtained by splitting the two versions at a more-or-less arbitrary point and rejoining with the versions crossed. (If you don't understand this description, try reading the article.) The upshot is that, although one copy of chromosome 1 is guaranteed to come entirely from your father, the parts of it that come from your father's father and your father's mother are highly variable. The same thing basically applies to every other chromosome except the X and Y sex chromosomes, where the story is more complicated. Looie496 (talk) 21:18, 2 July 2018 (UTC)[reply]

Short answer, no. They will usually be similar, but there will be differences since half their DNA is different and those different segments could have different ancestries. Dragons flight (talk) 22:17, 2 July 2018 (UTC)[reply]

Thank you for the replies. Bubba73 ^{You talkin' to me?} 22:26, 2 July 2018 (UTC)[reply]

Bubba73, my father and his siblings had analysis done on them at the end of last year, and they all came out differently. Yes, Dragonsflight's "similar" is correct, but they weren't identical. Nyttend (talk) 22:36, 2 July 2018 (UTC)[reply]

I had mine done and I've compared to my daughter and a first cousin on both sides (different cousins!). There are naturally commonalities and differences. Bubba73 ^{You talkin' to me?} 23:12, 2 July 2018 (UTC)[reply]

This is all going to depend very heavily on the precise analysis done by a company. Suppose they used three genes with alleles that came from Africa or Asia. Then 1/8 of the children of a purebred African-Asian marriage would be African and 1/8 would be Asian. Hence ... they use more markers. But only so many are available, and they aren't really so easily localized to one continent, but just have differences in frequency between continents. To decide how much each means you're making a model of what the historical genetic makeup of the continent was, and then of countries within it, which means defining when you are talking about (100% of New Jersey residents have New Jersey ancestry!). There's even some necessary revisionism involved (do the Irish have British ancestry, because their country was occupied by Britain, or (I think) once considered part of the Britannia Province of Rome?) The more I think about it the more the wheels come off this wagon, and there's a reason - because you don't inherit nations, you inherit genes. Wnt (talk) 11:59, 5 July 2018 (UTC)[reply]

The Romans didn't bother with Ireland, they called it Hibernia (winter land) which makes most land at that latitude laugh as to them the Irish winter is weak and mild like a little lamb. At least one Roman travelled to the west shore of Ireland (the Cliffs of Moher I think) and thought it was the edge of the World. Sagittarian Milky Way (talk) 17:48, 5 July 2018 (UTC)[reply]