Dominant White, Sabino-1 and Sabino

[quote=Jackie]I was wondering which breeds have been tested positive[/quote] Paint, Minis, TWHs, Missouri Fox Trotters, and others that are escaping me.[quote] and which breeds display the pattern and text negative.[/quote] All breeds display some sort of Sabino patterning, so I suppose every one. [quote] Also, are their breeds with horses that have test both positive and negative?[/quote] Of course, just like every other pattern, not every horse will have that pattern.
[quote]Are they thinking that all the dominate white horses found in the different breeds that it's been found are all different from each other? Unrelated? These white horses are so confusing :-?[/quote]Each DW FAMILY is a separate mutation even within the same breed, so yes to your question. There are currently 11 or 13 different DW mutations with each one starting with a different horse.

hmm... I don't think EVERY breed in the whole world has displayed sabino patterns. Has the welsh pony been tested positive?

Sabino is used as kind of a catch all BUT the only breed thought to not carry some type of sabino pattern is the Icelandic.

What about breeds that don't have pinto patterns or much white markings like fresions, norwegian fjords and breeds like that? I think I spelled those way wrong

Even people can have sabino: http://www.facebook.com/photo.php?fbid=…

Usually not as loud as these guys but often just a white spot on the forehead. NOT associated with blue eyes, for the record.

I forgot that my whole point is that all animals get random white markings that can spontaneously mutate into existence and then be passed along. That means that any breed COULD (most likely) suddenly show up with white markings, which I think people just shove into the category "sabino."

Friesians can get white markings, along with other completely solid breeds. I can't remember which breed it is (Fell pony???) that they'll actually note when they have white markings on the soles of their feet. I think this might be a really minimal form or white marking?

There are a couple of theories on white markings, one is that all white markings are the result of some form of white pattern gene with the very minimal forms due to seperate white supressors. Another is that minimal white markings are due to conditions in the womb and don't have to be related to a white pattern. I lean toward the former because the pattrns that we can test for do appear in very minimal forms (white spot on the botttom of the foot for frame) but we also know from clones that enviromenal factors do affect white markings. We probaby won't know the complete truth until we can test for everything. On my phone so I hope this makes sense.

I think it is possible for very minimal white markings to just happen without being caused by a gene. Some breeds of horse never have more than minimal white markings and these could easily be caused by the spread of melanoblasts simply not reaching right into the 'corners'.
I see lack of white not being due to white suppressors but rather colour enhancers, some people seem to think white markings on animals are like white painted on top of and covering coloured bits where really it generally represents places where the melanoblasts didn't reach for whatever reason.

IMO if white markings were caused by womb environment only and not genetic factors you would most likely start seeing white in places not on the face/legs. There would also be a lot more random white in horses like Fresians or Fjords where white is discouraged.

Just because a horse has white markings, I don't think it should automatically be labeled sabino. I could kind of understand that maybe one chin spot is a VERY minimum expression of sabino, but a stare or faint on a Fresian is not following the pattern. And the sabino patterns found in draft horses like shires and Clydesdale are so different than the pattern on Arabians that they have to be totally unrelated to each other. They need new names. Grouping everything to Sabino is like when everyone grouped everything to overo if it wasn't tobaino. That's why I wondering how many different breeds displayed sabino, since they're most likely not related

[quote=Third Peppermint]Even people can have sabino: http://www.facebook.com/photo.php?fbid=…

Usually not as loud as these guys but often just a white spot on the forehead. NOT associated with blue eyes, for the record.[/quote]

Oh this is great. I was trying to fin pictures of this before with no luck

White markings probably do need a new name, but we kind of need a generic name to cover all of the spontaneous mutations. Sabino has been a scapegoat catch-all term. I guess we could use "white markings" but that's a little TOO generic.

I am welcome to suggestions as to what we can call it. Maybe once our testing improves we can start to make new names for things.

Oh, and there is a facebook page for people with piebaldism where you can find many examples of white spotting in humans as well as family lines and whatnot.

[quote=RiddleMeThis]IMO if white markings were caused by womb environment only and not genetic factors you would most likely start seeing white in places not on the face/legs. There would also be a lot more random white in horses like Fresians or Fjords where white is discouraged.[/quote]

I'd think it would be a fairly unusual occurrence, and also would not be random- in horses the feet and central line of the face are probably the last place the melanoblasts reach before they proliferate as malanocytes, so a little hitch in the process, not necessarily caused by a specific gene mutation, might leave little white areas on the face or feet. This is only a guess though, even very small amounts of white might be caused by a mutation, just not necessarily one of the main ones.

[quote=Jackie]Just because a horse has white markings, I don't think it should automatically be labeled sabino. I could kind of understand that maybe one chin spot is a VERY minimum expression of sabino, but a stare or faint on a Fresian is not following the pattern.[/quote] Its already 1000% proven that sabino can be just as minimal as a single star. THAT is the minimal expression of sabino. Not a chin spot. [quote]And the sabino patterns found in draft horses like shires and Clydesdale are so different than the pattern on Arabians that they have to be totally unrelated to each other.[/quote] The white in drafts is most likely a form of Dominant White and not Sabino at all. That being said even the known Sabino has INCREDIBLY different phenotypes. [quote]They need new names.[/quote] No they don't. [quote]Grouping everything to Sabino is like when everyone grouped everything to overo if it wasn't tobaino.[/quote]
And no its not. Sabino covers a distinct type of pattern with a fairly distinct phenotype. Saying that we need a different name for it because it occasionally looks different is like saying we need a different name for Silver because it looks different in minis than it does in QHs. Or that we need a different name for frame because it doesn't always make a white pattern. It's not all about phenotype.

[quote]And the sabino patterns found in draft horses like shires and Clydesdale are so different than the pattern on Arabians that they have to be totally unrelated to each other[/quote]

Along the same lines as what RMT posted, what is labeled sabino in Arabians is often not sabino but DW or splash. Many of the white pattern phenotypes that were once labeled sabino are now DW and many of the more minimal patterns that are also called are probaly not sabino at all but splash. We see this when two minimal parents pop out a loud splash foal.

As far as the migration of melanoblasts, I agree that it the forehead of the horse and the legs are the last places that they reach. The question is what is causing them to stop the migration prematurely? It is just random? Or is it a white pattern?

[quote=RiddleMeThis][quote=Jackie]Just because a horse has white markings, I don't think it should automatically be labeled sabino. I could kind of understand that maybe one chin spot is a VERY minimum expression of sabino, but a stare or faint on a Fresian is not following the pattern.[/quote] Its already 1000% proven that sabino can be just as minimal as a single star. THAT is the minimal expression of sabino. Not a chin spot. [quote]And the sabino patterns found in draft horses like shires and Clydesdale are so different than the pattern on Arabians that they have to be totally unrelated to each other.[/quote] The white in drafts is most likely a form of Dominant White and not Sabino at all. That being said even the known Sabino has INCREDIBLY different phenotypes. [quote]They need new names.[/quote] No they don't. [quote]Grouping everything to Sabino is like when everyone grouped everything to overo if it wasn't tobaino.[/quote]
And no its not. Sabino covers a distinct type of pattern with a fairly distinct phenotype. Saying that we need a different name for it because it occasionally looks different is like saying we need a different name for Silver because it looks different in minis than it does in QHs. Or that we need a different name for frame because it doesn't always make a white pattern. It's not all about phenotype.[/quote]

Well, I don't know what you problem is, but no... Silver should not have different names because it's all caused by the same dilution. Since Sabino in Arabians and Draft horses can't be tested, there no way to say that they're related, and most likely they're not. So it makes no sense to give them the same name. And I thought dominate white was loosely defined as at least 50 percent white horse. I say loosely because there isn't a dominate white gene out there to make a rule so all these terms are just for our benefit. What causes white pattern in draft horses, who knows, but what I'm saying it's not the same thing that happens in Arabians and there for should be called something different because it IS something different. That's my opinion because things that are different make sense to me to be called something different. I don't know who you are to say NO to that

[quote=Jackie]Just because a horse has white markings, I don't think it should automatically be labeled sabino. I could kind of understand that maybe one chin spot is a VERY minimum expression of sabino, [/quote]

Actually I think chin spots are splashed white, as are a lot of the arab markings. And as already said, 'clydesdale sabino' is probably DW with some splash thrown in. Where as a white star could very well be sabino. Dominant white isn't about whether the horse is more than 50% white, they are a white pattern gene like the others and have more maximum and minimal expressions. But yeh until we have tests for all thse things we can only group them on similarities, and inheritence patterns we observe

[quote]And I thought dominate white was loosely defined as at least 50 percent white horse. I say loosely because there isn't a dominate white gene out there to make a rule so all these terms are just for our benefit.[/quote]

Dominant White is a mutation of the kit gene that causes white markings similar to what has always been called sabino in the past. The difference is that sabino needs two copies of the gene to fully express while DW only needs one (DW is homozygous embryonic lethal). There have been at least 12 DW mutations actually located by researchers, in breeds that include Arabians, TB, QH's, and Paints. It's not just a term used to define horses that are at least 50% white.

[quote=Jackie]
Well, I don't know what you problem is, but no... Silver should not have different names because it's all caused by the same dilution. Since Sabino in Arabians and Draft horses can't be tested, there no way to say that they're related, and most likely they're not. So it makes no sense to give them the same name. And I thought dominate white was loosely defined as at least 50 percent white horse. I say loosely because there isn't a dominate white gene out there to make a rule so all these terms are just for our benefit. What causes white pattern in draft horses, who knows, but what I'm saying it's not the same thing that happens in Arabians and there for should be called something different because it IS something different. That's my opinion because things that are different make sense to me to be called something different. I don't know who you are to say NO to that[/quote]
All of those reasons are why the researchers gave a number to Sabino 1. Because they believe there are multiple mutations that do the exact same thing. Its why all the DW (Of which they have found and located at least 12) have numbers. Because they are all different mutations that caused similar phenotypes. They DO have different names. DW1, DW2, DW3, ect ect. And that is why the Sabinos will all be named similarly.

I have my own theories for how white forms just from what I've seen. Especially on the tobiano brindle. It looks like the color develops fully and proliferates with the melanoblasts as Dogrose describes But I think something has to block that color from expressing in the hair and skin causing white patterns, not that it just doesn't reach those areas.

Especially roan with it's individual white hairs singled out and LP horses who's expressions of white change and vary over the course of their lives. Some LP horses 'reverse varnish' and gain back their coloration where it was once taken over by white. Some get repigmentation spots in their patterned areas that develop with age. Plus there are "late bloomer" LP horses who are born dark and can mature into full leopards. And their white isn't caused by roaning, it's a PATN gene. The color was under there but something blocked it allowing a white pattern to show.

" Because they believe there are multiple mutations that do the exact same thing. Its why all the DW (Of which they have found and located at least 12) have numbers. Because they are all different mutations that caused similar phenotypes. They DO have different names. DW1, DW2, DW3, ect ect. And that is why the Sabinos will all be named similarly."

Well I'm glad to hear that the dominate white mutations are being numbered. I'm would like to read more into that. I (this is my opinion so don't just dismiss it) Thank that labeling the sabino patterns by numbers will still make sorting out the patterns confusing. I'm horrible with numbers, so a name is much easier to remember. I understand agreeing on or even coming up with a new name would be difficult. I'm not sure how most of these names for horse colors come up, but it seems like most of them are spanish sounding. Though Sabino literally means pale red, or red roaning according to Dr. Spongenberg

http://www.duncentralstation.com/PDF/KI…

This is a little outdated as to the number of DW mutations, but it is great for a basic explanation of the KIT gene and why everyone is using DW and sabino with numbering rather than a bunch of different names. They are all a mutation of the same gene and have similar phenotypic expressions.

[quote=Threnody]I have my own theories for how white forms just from what I've seen. Especially on the tobiano brindle. It looks like the color develops fully and proliferates with the melanoblasts as Dogrose describes But I think something has to block that color from expressing in the hair and skin causing white patterns, not that it just doesn't reach those areas.

Especially roan with it's individual white hairs singled out and LP horses who's expressions of white change and vary over the course of their lives. Some LP horses 'reverse varnish' and gain back their coloration where it was once taken over by white. Some get repigmentation spots in their patterned areas that develop with age. Plus there are "late bloomer" LP horses who are born dark and can mature into full leopards. And their white isn't caused by roaning, it's a PATN gene. The color was under there but something blocked it allowing a white pattern to show.[/quote]

Some form that way- I don't see de pigmenting patterns as being true white spotting. All the de-pigmenting patterns occur in coloured areas where melanocytes exist, you can see this in an appy tobiano or roan tobiano for example. With roan something is switching some melanocytes off, same with appy, thats how re-pigmenting can occur, they get switched back on.
If you look at some white patterns they actually look like ink spreading on blotting paper. If all white markings were just caused by areas being switched off they would be more random and would be much more susceptible to re-pigmenting and the coloured areas to de-pigmenting.

Now that I read the link from monsterpony, how much of this information is outdated? Is there more Dominate White mutations found? To my understanding, it seems like difference between Sabino and Dominate white, that Dominate is more white with just one dose of the gene. Is it till believed that Homozygous to be fatal?

[quote]Now that I read the link from monsterpony, how much of this information is outdated? Is there more Dominate White mutations found? To my understanding, it seems like difference between Sabino and Dominate white, that Dominate is more white with just one dose of the gene. Is it till believed that Homozygous to be fatal?[/quote]

What monster meant was that the number of DW mutations actually located was a bit out of date. The rest of the information on that page is accurate. As far as I know the number of DW mutation actually located by researchers is up to 12. There are probably many more yet to be located.

The main difference between DW and Sabino is the method of inheritance.

Yes, DW has been proven by genetic researchers to be embryonic lethal. The only question is if a foal that was heterozygous for two different DW mutations could be viable for example a foal that was W[sup]4[/sup]W[sup]6[/sup]. The researchers couldn't or wouldn't make a guess on that one and there haven't been that many breedings between different DW lines.

Then there are the fairly recently mutated DW lines. Some haven't had the chance to be present in homozygous form in an individual so we don't know if all are homozygous embryonic lethal yet.

Dogrose thanks for the extra info! What are your thoughts on the brindle tobiano? I'm curious to pick your brain about him. ^_^