Science desk
< September 26	<< Aug \| September \| Oct >>	September 28 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 27

proteun

Which protein in dogs help them to smell so well?Acidic Carbon (Corrode) (Corrosive liquid) 12:21, 27 September 2020 (UTC)[reply]

The keen sense of smell of dogs has to do with the high quantity of Olfaction receptors they have. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:08, 27 September 2020 (UTC)[reply]

Baseball Bugs Thanks! Acidic Carbon (Corrode) (Corrosive liquid) 13:12, 27 September 2020 (UTC)[reply]

Acidic Carbon , see also More fat, less protein improves canine olfactory abilities (Cornell University, 2013). Alansplodge (talk) 13:30, 27 September 2020 (UTC)[reply]

Alansplodge Wow!But do dog olfactory cells work the same way?Acidic Carbon (Corrode) (Corrosive liquid) 13:39, 27 September 2020 (UTC)[reply]

Sorry, I can only tell you what is written in the article. Alansplodge (talk) 15:04, 27 September 2020 (UTC)[reply]

And anther advantage for dogs, is that their nose is often close to the ground, or other things. Graeme Bartlett (talk) 21:50, 27 September 2020 (UTC)[reply]

Dogs also possess a vomeronasal organ,^[1] an additional olfactory sense organ. (There is still debate over whether humans have one, but if so then it is at best rudimentary or vestigial in most humans and very likely hardly or only marginally functional.) But this, or their sniffing from a close distance, is not enough to explain that the canine olfactory sensitivity is up to 100,000 times that of the average human.^[2] One factor is the larger number of olfactory receptor cells, made possible by a vast olfactory epithelium.^[3] An olfactory receptor cell is specialized to respond to a specific odorant. Probably, there is a larger variety in the odorants canine receptor cells respond to, explaining the canine ability of discriminating between a larger variety of similar smells and following one specific smell trail. --Lambiam 09:44, 28 September 2020 (UTC)[reply]

Dogs have only 44 times as many olfactory receptors as humans, so there is no way that they have a sense of smell 100,000 times better. Abductive (reasoning) 10:11, 3 October 2020 (UTC)[reply]

What's the source for your conclusions? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:37, 3 October 2020 (UTC)[reply]

I didn't make any conclusion. But I do know that all these "dogs smell 50,000/100,000 times better than humans" memes have been circulating forever with no support. Abductive (reasoning) 16:10, 3 October 2020 (UTC)[reply]

Do siblings with more similar chromosomes look more similar?

Given the size of the World's population, there should exist a few siblings with 15 identical chromosome pairs. Do such siblings look like identical twins? Count Iblis (talk) 19:59, 27 September 2020 (UTC)[reply]

Chromosomes aren't really inherited as a whole. Crossing over and spontaneous mutations mean that the chromosomes you inherited from each parent do not exactly match the ones that they have, much less the ones that your siblings would inherit. --Khajidha (talk) 20:32, 27 September 2020 (UTC)[reply]

To build on what Khajidha said, it despite the size of the world population, it is incredibly unlikely that any siblings share identical chromosome pairs outside of cases such as identical twins. That there are 7 billion some odd people doesn't make it appreciably likely that even a single non-identical twin set has that level of genetic similarity. Even if you want to consider spontaneous mutations rare (which they aren't, it's just that most of the time the results are benign), chromosomal crossover during sexual reproduction is NOT rare. The same goes for genetic changes during meiosis in the production of gametes. If the gametes themselves are not genetically identical even within a single parent, then offspring produced with different gametes, even from the same set of parents, stand basically no chance of being genetically identical. --OuroborosCobra (talk) 00:22, 28 September 2020 (UTC)[reply]

Just to give a notion of the size of the scales here, there are about 3,000,000,000 base pairs in the human genome. Given that there are 4 different bases, that means there are 4^{3,000,000,000} possible DNA sequences, a number so stupendously large that it would take longer than the entire history of the universe just to write out the digits. The chance that in a population of 7,000,000,000 people, any two of those (even non-identical-twin siblings) would have functionally the same DNA is so close to zero as to not even be considered different from zero. --Jayron 32 11:36, 30 September 2020 (UTC)[reply]

These calculations are not based in biological reality. We suspect that only a tiny subset of genes are involved in appearance, and many of these group together on chromosomes. Nearly all genes are functionally identical within a species. Most changes to base pairs have no effect, and there is, on average, only one crossing over event per chromosome during meiosis. People are able to detect when two siblings resemble each other more than a third sibling, and full genome sequences would reveal that they had appearance genes in common. Scaled up and with simpler phenotypic traits that are easier to quantify, this is how scientists find out which genes do what. Abductive (reasoning) 10:05, 3 October 2020 (UTC)[reply]