Wikipedia:Reference desk/Archives/Science/2020 September 1

= September 1 =

epidemiology of Covid19 in United States
Supposing there were a vaccine created for Covid-19 in the next few years, but only 40% of Americans took it, maybe because of genuinely harmful side effects, or pseudoscience, or whatever. Would the fraction of Americans who had been infected from Covid at least once eventually approach 60%, assuming the vaccine was almost 100% effective?Rich (talk) 07:48, 1 September 2020 (UTC)
 * That's not how herd immunity works. Somewhat simplified, if R0 is around 3 (which it seems to be for COVID-19), then every patient infects 3 others in a "virgin" population. If 2/3rds of people are immune for any reason, then that patient will only infect one other - the other two "transmission opportunities" fall on fallow ground. In that case, the number of infected will not grow (and if the number of immunes increases further, which it will naturally, each patient will infect less than one new case, and the number of new infections will go down exponentially). That's why basic herd immunity is computed as 1/R0. So you need 40% of vaccinated people, plus 26.6% of other immunes (i.e. people who recovered from infection). And if you manage to decrease actual R by other means (masks, social distancing, quarantine, ...) you may get away with even fewer cases. All this is assuming that  recovered COVID patients are largely immune - something that seems likely, but we are not quite sure of. --Stephan Schulz (talk) 08:44, 1 September 2020 (UTC)
 * A relevant term here is "herd immunity threshold" (HT), which is the fraction of the population that needs to be immune for an infectious disease to push the effective reproduction number below 1. HT equals $1 – 1/R_{0}$, the complement of $1/R_{0}$. It is usually expressed as a percentage, so if $R_{0} ≈ 3$, HT is about 67%. There are a few documented cases of recovered patients who were re-infected. The immunity conferred by vaccines does not last forever either, which is why some experts are warning COVID-19 may perhaps never be eradicated completely. --Lambiam 09:46, 1 September 2020 (UTC)
 * Notice that even though the infected population goes down once the immune population reaches 1-1/R (whether by vaccination or going through the disease) the epidemic will still infect a few people while dying down, so the eventually-infected population is higher than 1-1/R-vaccinated. For the gory mathematical details (under certain assumptions etc.), see the $$r_\infty$$ in Compartmental_models_in_epidemiology (the model does not include vaccination during the epidemic but I would conjecture the answer is not too wrong if you take $$r_0$$ as the proportion of vaccinated). Tigraan Click here to contact me 12:54, 1 September 2020 (UTC)

Deer and goat hybrid is possible?
I've heard it's written in Mishna that it's possible but I'm not sure if it reflects reality or science. --ThePupil (talk) 12:26, 1 September 2020 (UTC)
 * It could be possible, but i wouldn't bet on it. Deer and goats are in different families, (Cervidae,Moschidae,Tragulidae) for deer and Bovidae for goats, so the cross would be an Interfamial hybrid. Zindor (talk) 12:43, 1 September 2020 (UTC)
 * It's very unlikely, given how rare interfamilial hybrids are. Most hybrids can only occur within the same genus, and I can't think of an interfamilial hybrid in mammals.  List of genetic hybrids has none listed.  -- Jayron 32 12:47, 1 September 2020 (UTC)
 * Thanks. Just want to note that Horses and donkies are also from different families, and still we may see the results exist as mules or hinnies.--ThePupil (talk) 14:59, 1 September 2020 (UTC)
 * They are absolutely not from different families. Horses and donkeys are both from the same genus even, Equus.  As I said, there are no examples I can think of for viable mammal hybrids from different families.  There may be some from different genera, but even so, the vast majority are different species within the same genus.  -- Jayron 32 15:07, 1 September 2020 (UTC)
 * I thought they are different, because of what I read on this article on Wikipedia: "Donkeys have 62 chromosomes, horses have 64 chromosomes, and mules or hinnies have 63 chromosomes". So they are from the same family with a different number of chromosomes? --ThePupil (talk) 15:19, 1 September 2020 (UTC)
 * Yes, the number of chromosomes is not necessarily consistent between species even if they are in the same genus. In the case of horses and donkeys, they are both members of the same genus, being Equus.  Family is one layer yet again higher up the Linnean classification system above genus.  So everything that is part of the same genus is also part of the same family (and class, and order, and phylum, etc)  -- Jayron 32 15:42, 1 September 2020 (UTC)
 * Thank you. I've learnt something new. So basically we cannot say surely that cross between deer and goat can be. Right? Do we know an animal hybrid of two families?--ThePupil (talk) 19:52, 1 September 2020 (UTC)
 * No, no one in history has ever produced a cross between a deer and a goat. You are incorrect on that.   Deer and goats are members of entirely different families, deer being members of the Cervidae family and goats are members of the Bovidae family.  Given that, as I noted above, there has not ever been before a mammalian hybrid from such distantly related animals, it is unlikely there to ever be one in the future either.  -- Jayron 32 12:13, 2 September 2020 (UTC)
 * Some wild horses also have a different number of chromosomes. Ruslik_ Zero 18:48, 1 September 2020 (UTC)
 * Deer-cow Hybrids seems somewhat controversial. Alansplodge (talk) 11:45, 4 September 2020 (UTC)

Do carrot tops contain toxic alkaloids?
The section § Consumption of the Wikipedia article on carrots states that "some sources suggest that the greens contain toxic alkaloids", citing two sources. Maybe I am overlooking something, but I cannot find this claim in either source. Is there some scientific basis for this – other than that almost any vegetable contains trace amounts of alkaloids? --Lambiam 15:05, 1 September 2020 (UTC)
 * Some possible additional sources can be found here. This source here states that the alkaloids in question are pyrrolidine and daucine.  -- Jayron 32 15:10, 1 September 2020 (UTC)
 * So "all alkaloids are bad because substances like caffeine and cocaine are alkaloids". Next thing you know people will start snorting carrot tops instead of smoking banana peels. --Lambiam 07:37, 2 September 2020 (UTC)
 * I'm afraid I said nothing of the sort. I'm not sure where you think I did?  -- Jayron 32 14:43, 2 September 2020 (UTC)
 * Lambiam wasn't quoting you, but rather the piece from carrotmuseum. Even there it was described as a "myth".
 * I'm curious now what "daucine" is. I don't see any recent entries on a naive search.  "The Plant Alkaloids", by Thomas Anderson Henry, whoever he may be or have been, says the following, in a typeface that suggests it's a rather old book:
 * "Carrot leaves contain, according to Pictet and Court, pyrrolidine and an alkaloid, DAUCINE, C11H18N2. The latter is a colourless oily liquid, b.p. 240o–250o, [a]D +7.74o in ether, having an odour like that of nicotine, but which does not give the pyrrole reaction."


 * No structural formula is given. My guess would be that this substance now has a different name, which is why I don't find recent info on it, but I don't know what it would be.  If it could be found, we should create a redirect. --Trovatore (talk) 17:44, 2 September 2020 (UTC)
 * SciFinder lists that name as having CAS# 1399-02-6 with a matching molecular formula and approximate boiling point (corrected from a different pressure), but no structure or other synonyms. DMacks (talk) 03:38, 3 September 2020 (UTC)
 * Thanks. Seems to be behind a paywall with no obvious price list :-) --Trovatore (talk) 05:54, 3 September 2020 (UTC)
 * This chemicals list, volume A–G of a two-volume book, has "daucine" as the only name for [1399-02-6]. The number does not occur in the H–Z volume, so it seems that there is no current synonym and that the dearth of results is due to its lack of popularity. --Lambiam 07:18, 3 September 2020 (UTC)
 * The name undoubtedly derives from the genus name of the binomial name of the carrot, Daucus carota. --Lambiam 07:31, 3 September 2020 (UTC)
 * The Dictionary of Food Compounds gives structural descriptions where known, but has for daucine: "Struct. unknown". --Lambiam 07:41, 3 September 2020 (UTC)
 * This is the publication where Pictet & Court announce a novel alkaloid and name it daucine. --Lambiam 08:37, 3 September 2020 (UTC)
 * That's cool. Fun to look at this old stuff sometimes.  I'm a little shocked that no grad student has bothered to work out the structure in all these years.  Could be a master's thesis, maybe? --Trovatore (talk) 18:20, 3 September 2020 (UTC)
 * It was a direct quote from the carrotmuseum page – the top result of the Google search. While it mentions "This popular myth", presumably (the antecedent is not made explicit) referring to the idea that carrot tips are not edible, the bit I quoted about caffeine and cocaine is in a different section and not identified there as being questionable. --Lambiam 07:08, 3 September 2020 (UTC)
 * Ah. I think this was the page I saw, or possibly a mirror of it.  It says Myth #1: Carrot greens contain alkaloids (which are toxic bitter compounds produced by a plant) and all alkaloids are bad because substances like caffeine and cocaine are alkaloids.  Looks like it was directly quoting, and attempting to refute, the carrotmuseum line. --Trovatore (talk) 07:16, 3 September 2020 (UTC)