Wikipedia:Reference desk/Archives/Science/2020 October 16

= October 16 =

Is it possible to sequence degraded genomes by taking many samples?
I know that DNA degrades over time, but it degrades equally throughout the body? Would it be possible to take ten, a hundred, a thousand samples or more than one organism in a zoological sample, be it a Pleistocene animal or a well-preserved or poorly preserved hundred-year-old organism, and sequence its entire genome? How much would this cost? 179.240.185.82 (talk) 12:40, 16 October 2020 (UTC)
 * Theoretically yes, but I am not sure it is of any practical significance as DNA degrades too fast. Ruslik_ Zero 14:13, 16 October 2020 (UTC)
 * Yeah, sometimes it's gone completely after only 300,000 years. 108.18.193.173 (talk) 04:51, 18 October 2020 (UTC)
 * Possibly the currently leading scientist in this area of study is Svante Pääbo: you might try following up links in that article to see if they lead to any more specific answers. My own extremely lay understanding (gleaned from my amateur interest in paleoanthropology) would lead me to reply "something kinda sorta like this is already being done, but it's way more complicated than that." {The poster formerly known as 87.81.230.195} 2.122.178.0 (talk) 21:10, 16 October 2020 (UTC)
 * Yes, all sequencing, not only of old genomes, is made by repeating the sequencing several times with different cells or individuals, this is necessary in order to recognize sequencing errors and random variabilty like Single Nucleotide Polymorphism. The result of any single sequencíng of a genome fragment is called a read and the number of complete sequences is called coverage, see Coverage_(genetics)
 * Today sequencing one genome costs round $1,400 2003:F5:6F11:9700:E984:90F6:23B5:2DB4 (talk) 16:03, 17 October 2020 (UTC) Marco PB


 * Returning to your original post re DNA degredation: this is hastened by higher and varying temperatures, and exposure to moisture, which is why it's harder to get good samples of of old DNA from more tropical areas, as opposed to northerly dry caves. Another major factor is contamination by the DNA of microbes and other fauna that may be present in the environment, not to mention that of the archaeologists and others who handle the specimens! Some of the oldest recoveries of well-preserved DNA have recently been made by drilling into the interior of intact teeth (which themselves preserve better and longer than the rest of the body). {The poster formerly known as 87.81.230.195} 2.122.178.0 (talk) 12:13, 18 October 2020 (UTC)

thank you, you were of great help. — Preceding unsigned comment added by 179.240.176.53 (talk) 22:55, 18 October 2020 (UTC)

Impulse of black powder rocket motors
Our article Black powder rocket motor states: "The E class 24 mm motors have a maximum thrust between 19.4 and 19.5 N, a total impulse between 28.45 and 28.6 N·s, and a burn time between 3 and 3.1 seconds." However, 19.4 * 3 = 58.2, which would suggest that the motor should have a much higher impulse. My guess is that the impulse is calculated by integrating the force with respect to time, and since the actual force at any given moment is considerably less than the maximum for much of the flight, the reported impulse is lower. Is this correct? -- Puzzledvegetable Is it teatime already?  16:17, 16 October 2020 (UTC)


 * Peak power (or peak thrust, in this example) is not identical and is quite a lot higher than the average power (or average thrust, in this example).
 * If the engineering data sheet was very extraordinarily detailed, it could plot (or otherwise specify) the thrust as a function of time; and you could more correctly estimate a total impulse by integrating the thrust over time.
 * From NASA's Glenn Research Center educational outreach for K-12 students ("the Beginner's Guide to Propulsion"), here is the general thrust equation, using notation that I'd normally expect to see presented to college-level physics or math students. Perhaps the next generation is more mathematically prepared than we have all feared!  This presentation also introduces some of the specialized simplifications to the basic general equations of kinematics that are often nominally used to specify rocket impulse.
 * Nimur (talk) 16:45, 16 October 2020 (UTC)