What genes make what white?
Okay so for my college equine class I'm going to do a project/PowerPoint over what genes make what white.
So, can somebody point me in a direction on what the sabino, splash, frame, Tobiano (am I missing any?) look like?
I'm also going to use pictures for examples.
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I could go on an on about his topic so I will try to stay on track as much as possible :) I know a lot about these kinds of genetics but I am not an expert! I can give you a good outline though!
I'm not sure what you mean by "what genes make what white" because white is not really a color more like lack thereof. To truely understand the different coat patterns (overo, tobiano, sabino etc . . .) you need to understand what causes the disturbance in melanin.
The appearance of "white" in pinto/paint horses is related to genetic mutation called Leucism. UNlike albino, which most people are aware of, does not exist in the equine world, rather a specimen has not yet been reported. Leucism, however, is similar to albino in that albinism is solely a lack in melanin - black and brown pigments (eumelanin) - for both mammals and reptiles; where leucism is a lack in all melanin pigments in every species - the gene behaves the same in every animal.
In horses, there are two main melanin pigments: eumelanin a.k.a. agouti (bay/black) and phaeomelanin (non-agouti/chestnut).
As a side note, these genetic phenomena which are overwhelmingly present in equine, show up in other species too, however, affect such species differently. For instance, for whatever reason there is a link between medecine hat paints (another form of leucism) and deafness, however, in ball pythons (python regius there are no noticeable defects linked between animal and mutation.
Here is an example of a leucistic ball python (a pinto python lol)
and here is a leucistic deer (I'd say it looks similar to an overo pattern?) : http://img443.imageshack.us/img443/9711/lucydeer.jpg
Next, another melanin modifier, for lack of a better word, is the dominant white gene, not to be confused with lethal white (homozygous form of overo) - there are eleven different forms of D. white!
Here is an D. white thoroughabred stallion:
NOW for the actual variety of inheritable patterns: this is a hotly debated issue between horse breeders and scientists. For example, Quarter horses are supposed to SOLID, however, every now and then a foal pops out with a belly spot and to my knowldege would make the foal unregisterable as ONLY a QH but would have to be double registered as QH/PAINT. (maybe some breeders can help here?). But anyway, the parents of this foal would more than likely be carrying some form of the sabino gene.
Hence, we see paints with "roaning" not to be confused with a "red roan" or "blue roan" (different kind of roan), example: http://img31.imageshack.us/img31/4995/roaningsabino.jpg
Some horses who carry the sabino gene (heterozygous) will display this roaning of white hairs.
I know I am forgetting something, or a lot, so please message me of w/e if you ned moe clarity - I can help :)
I like what the above has said, and like stated, you missed DW- which isn't always a wholly or majority white horse- ex. the whole Puchilingui line [<3] and I think there is even a whole other separate line of DW TB's...?
I have lots of pictures, but if you need the sources/references or permission to use, I don't have any, but it wouldn't be that hard, given the cool google image URL search tool :3
In addition to Dominant White's maximum expression causing an entirely white horse, like what's posted above, sabino's maximum expression also causes a total white. Maximum sabinos have dark eyes if there is not another gene present.
Splash will also cause an entirely white horse in the right combination.
Can't Hear Guns, if I remember correctly, is positive for all three mutations of Splash currently testable. I don't remember her zygosity of any of them though. She's entirely white and deaf (hence her name :-P). Calla is genetically a bay under the white although she appears to be a double cream dilute with her pink skin and blue eyes.
Frame in its homozygous form causes a nearly entirely white (some do have small spots of color) or entirely white foal, for what it's worth. That foal will die, but it's still a white horse.
This filly was a LWOS foal
Hopefully these help and you can educate people more. One of my professors last year used a very old, outdated book and taught that grey and white are only different because greys have dark skin and whites have pink skin. ..This is coming from a textbook that also said grays are ALWAYS born black.
Funny you mention that issue with your professor - In my sophomore year (2009) my biology teacher was under the impression that when you mix a "white" horse with a black horse you get a piebald . . . lol I raised my hand and said, "Mrs. Kyle, that is impossible, the horse depicted in the book is clearly gray and mixing two solid coat colors doesn't create an animal expressing piebaldism unless it is carrying a gene which causes such a mutation." She also believed that all "white" animals were albino . . . She didn't believe me and mocked me in front of the whole class. Later that night I sent her an email with over ten sources proving I was right and that she was teaching out-dated materiel.
Since then I always wondered what else in incorrect in our school books that cost us an arma and a leg :evil:
Needless to say, her and I didn't get along very well lol
I mean, my teacher was an old woman who retired the next year (thank GOD) but I can't understand how this S*** still goes on in a college setting. It's like, when was the last time YOU checked YOUR SOURCES?
I give up on life . . .
Thanks guys!!! VERY informative!! Lots of stuff that I will certainly use!!
I guess what I kind of meant...is like...when your looking at what I guess you would call a solid, how can you tell what gene is causing the shape of the white pattern (blazes, socks, etc)? Like I read that the sabino will make more symmetrical face markings, which doesn't make sense because theirs normaly have jagged edges when it's on their bodies...
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Bumpity bump bump.
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