This is quite a feat of scientific depth meets subtle snark meets parody of British quirkiness. It perfectly captures how the story itself makes you think both "that's silly" and "of course they'd do that, they're scientists!"
> "As someone puzzled what left vs right meant in the nyt article its that the coils are not symetrical but bulge out to one side "
I don't think that is the explanation. Looking at Jeremy head on, you can see his shell spirals out to his left (our right) - with other snails, the shell spirals out to their right, as you can clearly see on the baby snail crawling on Jeremy in the initial article photo and also in another photo, where Jeremy is crawling on top of another snail (There is probably a joke in there somewhere!)
> Jeremy won international fame for a mutation that caused his shell to coil left instead of right. For years, people searched for another lefty snail with which he could mate. Shortly before his death, she was found.
Since most of the snails (all?) are hermaphrodites isn't this use of "he" and "she" wrong? (or at least misleading?)
> All of the babies were born with a right-handed shell. This means the gene causing a snail’s directional twist (and body asymmetry in other animals), described last year in Current Biology, could take more than a generation for its recessive form to appear.
This doesn't make any sense. Is the left handled shell caused by a recessive gene? If this were the case, the offspring of two left handled snails should be also left handled. Is it possible that this was not caused by a genetic mutation, and it's just that a tiny amount of normal snails get the wrong orientation?
Could be multiple genes. One snail has L1/L1 and L2/R2 for a right-handed shell, one has R1/L1 and L2/L2 for a right-handed shell, and one of their children has L1/L1 and L2/L2 for a LEFT-HANDER!!!
Just as an example. It definitely does not work exactly like that, which is about as much as I'm confident in saying on the subject.
The article in Current Biology is about a single gene.
In your example the R1 and R2 genes are dominant, and L1 and L2 are recessive. In you model, if two left-handed snail mate, all the offspring will be left-handed.
I'll try to fix your table, but I prefer to use white as the "default" color.
I'm not sure about anemones. One possibility is that the color depend only of one gene that has three variants (alleles).
* White (recessive): "w"
* Red (dominant): "R"
* Purple (dominant): "P"
The table is:
| Genes | Result |
| ww | WHITE |
| wR or RR | RED |
| wP or PP | PURPLE |
| RP | PINKISH |
Other possibility is that there are two genes that produce the color. Each one has a dominant variant that produce the color and a recessive variant without effect.
* White: default color, no gene for this
* Red: "Y"es (dominant) -or- "n"o (recesive)
* Purple: "Y"es (dominant) -or- "n"o (recesive)
The table is:
| Red | Purple | Result |
| nn | nn | WHITE |
| nY or YY | nn | RED |
| nn | nY or YY | PURPLE |
| nY or YY | nY or YY | PINKISH |
Another possibility is the opposite case, that there are two genes that produce the color. Each one has a recessive variant that produce the color and a dominant variant without effect.
* White: default color, no gene for this
* Red: "y"es (recessive) or "N"o (dominant)
* Purple: "y"es (recessive) or "N"o (dominant)
The table is:
| Red | Purple | Result |
| yN or NN | yN or NN | WHITE |
| yy | yN or NN | RED |
| yN or NN | yy | PURPLE |
| yy | yy | PINKISH |
Or there can be one gene that has a dominant allele that produce color and other gene that has a recessive gen that produce color. Or two genes with three alleles, or more genes, or more alleles, or ...
But in any of these cases, the sentence in the article makes any sense.
One is wrong: either the table, or our "opinions" about genetics. The table is freely quoted from a well-known research done in my country during the 70's. However, I cannot find a reasonable reference to the original research, which should settle things. All I could find are citations of it in non-academic context. I'll try to contact the author and get my hands on the actual paper.
Even if I can't cite that specific table... it's extremely easy to find other examples just by digging into dominance hierarchy examples. And there are 3 loci in the table, not 2.
My first example is essentially equivalent to the AB0 group system. (White is 0, Red is A, Purple is B, Pinkish is AB.) A and B are dominant the lack of A and B is recessive. The AB0 is slightly more complicated, and mix some parts of my second example. https://en.wikipedia.org/wiki/ABO_blood_group_system#Genetic...
But, seriously, maybe it starts off really small and is a conservation of angular momentum thing, sort of like how most solar bodies orbit counterclockwise?
Only really small and, well, probably pretty slow. Something like a small grain of sand could maybe make it spin the other way?
Do keep in mind that I'm a mathematician. I haven't actually taken a bio course since about 1983.
I seriously wonder if it's something like a lump of skin or dirt that makes it go the opposite direction, or the direction of least resistance. Y'all busy looking at genes and stuff. I am gonna stick with simple.
It should be noted that my last bio course was well before the human genome was sequenced. I doubt they'd even done snails.
Yeah, I'm sticking with that. It's either that or aliens.
For the snails, probably you mean something like "initial break of symmetry".
In the initial steps of the embryo, it must define the front-back, top-down, right-left axis. (I'm not sure about the technical names.) IIRC, each one is defined by some gradient of chemical signal, they are not mechanical, but I'm not sure. https://en.wikipedia.org/wiki/Morphogenesis
Anyway, it would be a nice experiment to twist a snail embryo and see the development. In particular, the snail of the article has the reproductive and internal organs in the opposite side of most snails. What happens when you twist a snail embryo, do the internal organs get the mirrored position too???
It could also be that it's not a simple dominance trait, or even that you need n different locations to be heterozygous or something like that. In any event, the fact that there was a cluster of them on a farm means there's a good chance there's a genetic component.
Yuk yuk yuk. Offspring are all right. Very interesting though. 300 offspring, both parents left-y, but all offspring right-y. It seems curious that left-y is so rare and according to the article additional genetic studies are needed before the left-y cause is determined. Maybe it isn't genetic, but a rare quirk of development.
I was wondering why right-y is so prominent, but if there are physical limitations during mating between left vs right then one would naturally emerge. No mentions of alternate snail species in the article with left-y shells, but apparently left vs right shells are distinguishing features of gastropods (land and sea snails).
An interesting natural constraint on design. Edit: and by design I mean constraint on emergence / naturally restrained emergence, not some externally imposed design.
It seems curious that left-y is so rare and according to the article additional genetic studies are needed before the left-y cause is determined. Maybe it isn't genetic, but a rare quirk of development.
My wild guess, based on only a primitive knowledge of genetics and with analogy to computing, is that although DNA is highly "error-corrected", very very rarely this fails and a "bit flip" that reverses the shell goes through uncorrected.
It depends on the gasteropod species. Some species are mostly dextrogirous and other mostly levogirous. Nobody knows why.
Being one or another is a barrier for reproduction and this is important for the creation of new species of molluscs. A big and very interesting group of animals comprising around 70.000 different species of snails (vs around only 3000 extant mammals instead).
I couldn't care less about british politician jokes. Is more interesting to remember that there is a market for mollusc shells, and rarest items can be sold for a lots of money. Is sort like the valuable stamp with printing error.
It can be that multiple independent recessive mutations can cause leftyness. So if the parents don’t have the same lefty-genes, then the offspring will merely be carriers, but will look normal.
