Detangling the all new CORIN stuff today! This is important enough and long enough that we're getting genetics on main. This is going to be my masterpost until I get an article up on the main site about it.
For those not in the loop, sunshine in Siberian cats has recently been mapped to the CORIN gene, the same one that causes golden tabby tigers. An additional allele, extreme sunshine, has also been identified. And, "copper" phenotype golden British Shorthairs have been identified to have yet another mutation! All of these are recessive to the standard phenotypes.
Standard Golden - Found most famously in British Shorthairs, but also present in other breeds. It is a black-based tabby with the background color being golden and the markings being their normal black-based color. It also comes in shaded and tipped varieties, where we get less and less of the residual black-based markings.
Sunshine - Found in Siberians. Looks very similar to golden, but the hair is always pale to the root and they lack the dark nose rim found in most tabbies. Visible difference between those homozygous for agouti (standard sunshine), and those carrying solid (dark sunshine).
Extreme Sunshine - Sunshine with minimal markings, similar to the golden tipped phenotype.
Copper - Found in BSHs. Goes by several other names at this point, but I have consistently used copper so that's what I'm sticking with. It is golden tipped with almost no residual black, and the underside of the cat may become very pale.
The researchers have decided to use the symbol wb for CORIN, but I strongly disagree with this. "Wide band" has long been used as the name of the trait causing standard golden and silver shaded and tipped phenotypes, and has been generally accepted to be polygenic for some time. Some people still choose to use Wb for standard golden as though it is incomplete dominant, or else use symbols such as Wb+, Wb++ to track it. Even though CORIN causes "wide banding", it is distinct from the existing concept of the wide band trait.
What gives me the authority to coin a new gene symbol? Well, I've done it before when I needed to (Bengal Modifier is my doing) and people don't seem to mind. I don't expect it to catch on with researchers, but hopefully I can provide a nice alternative for breeders and hobbyists.
G is a nice candidate since it can stand for golden, and it's not currently in use for any cat genes. It was previously used for Birman gloving, but since that has been mapped to KIT, gloving now shares a locus with white spotting and dominant white. It's in my interest to keep any subscripts and superscripts short, since I can't use them in the dropdowns in my calculators and guarantee they'll be readable to everyone. So I want the symbols to be as short and clear in plaintext as possible.
For now, I'm going with G > gsh > ge > gc, corresponding to the currently used sequence WB > wbSIB > wbeSIB > wbBSH. Proper writing of all these is technically subscripts, but I usually end up leaving symbols as plaintext in my writings for readability. The dominance hierarchy of the lower alleles is based only on phenotype, and only exists because I need to have some order for them.
Note that the dash may stand for any lower allele.
G- : No mutation. Still may be standard golden if they have high wide banding polygenes.
gshge : Intermediate between sunshine and extreme sunshine, as they are confirmed to be codominant.
gshgc, gegc : Mystery phenotypes, may never be combined since sunshine and copper are both breed-exclusive as of now. When I add them to the calculator (soon!), I'll simply note them as "sunshine-copper" and "extreme sunshine-copper".
