Talk:Equine coat color genetics

Comment

the following link has the most informative and easy-to-understand explanation of equine color genetics that I have come across: http://www.equinecolor.com/color.html

Recent Edit

I have revamped the page. It still needs work, and especially pictures inserted to make the concepts clearer. The curent version is based on http://dreamviewfarm.com/genetics.html. As author of that site, anyone wanting to take the time to copy the pics from there to here is welcome to.

Accuracy of article (Comment recently restored)

I have recently been researching the genetics of horses, and have found this article to be one of the least accurate I have come across. Although much of it is correct, it still states many theories that have been disproven for as long as a decade in some cases. I am currently writing an article on current horse genetics, and will post it here once it is complete. In the meantime, anyone researching horse genetics is recommended looking elsewhere. Diamond Phoenix 08:01, 16 September 2006 (UTC)

Don't just slam, provide some basic evidence and recommend an alternative link, then. If you are so very knowledgable, you can surely do this in about 30 seconds. Best to be positive. Montanabw 05:57, 1 November 2006 (UTC)

WP:CIVIL, please. riana_dzasta 02:59, 2 November 2006 (UTC)

Research issues

Noted earlier comment since removed by poster (See 'Accuracy of Article'), though it worth resurrecting for comment.

Suggest that it might be useful to explain what and how various theories are "outdated by 10 years" in the article and provide some links to current research so that those of us who care can take a look and see what kind of consensus can be reached. My point is merely that we float test balloons before diving in with wholesale edits of what clearly was an article that someone took a LOT of work to create.

I find the genetics of color quite interesting and a field that has changed beyond recognition since I took a class that discussed genetics during the 1980's. I am not surprised that even now there are still changes and debates going on...but I have also seen some head in the sand attitudes amongst people who dislike the revelations of modern genetics and attack the science itself. (Thinking here of the early days of HYPP being linked to Impressive as an example.)

I am not a geneticist, I am just a horse person with a penchant for wordsmithing and my (warning: bad pun coming) horse in this race is to try and separate what is POV from what is flat-out inaccurate (amazing how often people confuse the two). If I am convinced that something is the consensus of modern science, I am happy. If not, I like to see the various points of view presented so that people can look into the issue for themselves. (Like the eternal debate over on the wild horse article over whether equus ferus is or is not the same as equus caballus...sigh...everyone argues, no one cites to research. How can we laypeople decide if we can't review the research others have done? Arrgh!)

Personally, I have yet to see a good research citation on the question of dominant white (WW) as a lethal, as contrasted with Lethal White Syndrome (OO). At this point, it is my understanding that both exist, but I have also seen (though am not yet convinced) some arguments that there is no such thing as the W gene at all, that all "white" horses are so-called fully-expressed Pintos...curious to hear what folks think? Montanabw 00:17, 17 September 2006 (UTC)

White Genes

Very little has actually been published on the subject of albinism in horses. One paper claims to have found the genetic marker that coincides with the White gene, but their evidence is doubtful, and the article has received no citations. http://www.blackwell-synergy.com/doi/abs/10.1111/j.1439-0388.2004.00481.x?prevSearch=allfield%3A%28white+genetic+mapping+horse%29 (Sorry: restricted access to full article.) If anything, they seem to have mistaken the sabino gene for the White gene. My discusions with experts in the field suggest few, if any, see the White gene as a plausible theory.

Current genetics tells us that horses that appear white are generally not albino, but instead contain genes for localised albinism, such as the leopard complex, the sabino complex, or various others. In these cases the white markings are fully expressed, and it is almost impossible to find any pigmented coat on the horse. This is not, however, considered true albinism, such as that supposedly caused by the White gene. Additionally, when many dilition genes are present, it is not possible to detect the presence of any pigment, and the horse appear white. This is not considered to be a form of albinism.

Currently the White theory states that the white gene is a dominant trait, so that ww codes for non-white, Ww codes for a completely white horse, and WW codes for a completely white horse with a lethal genetic illness (Lethal White Syndrome) that causes it to die soon after birth. By this theory, both parents of a LWS foal must be completely white, yet this is almost never the case. Instead, both parents have only small patches of white, caused by the Overo gene. (In very rare cases the overo gene is not present, although the horse still has the gene that codes for LWS.) Now that a genetic test exists for Overo, it has been confirmed that all LWS foals are OvOv and appear completely white, and both their parents are usually Ovov.

Since genetics tests have proven that it is not the White gene acting to cause all the traits that we have previously associated with the white gene, then this seems to be sufficient proof to say that it doesn't exist.

In case you're interested, Animal Genetics, Inc, is one of the organisations that offers genetics testing for the overo gene. You can read more about it here: http://www.animalgenetics.us/LWO.htm Diamond Phoenix

I know UC Davis does testing also. My understanding is that lethal white syndrome is NOT in any way linked to the W gene, even if it does exist, but instead is the gene (I have seen it called both "O" and "L")(?) associated with the "frame overo" pattern (though Paint breeders have hysterics when you way this, and it IS true that LWS occurs in Tobianos and even solids, as my understanding is that it's only lethal when homozyous). What we DO have, however, is two different lethal conditions. One is lethal albinism where foals are usually born dead, unlike LWS foals, who are born alive, but with the genetic flaw that results in either natural death or euthanisia shortly after birth. The "lethal albino" (for lack of a better term) is really interesting because I haven't heard it described as part of LWS, and many "white" horses out there produce offspring who are not Pintos, thus putting the "all white horses are maximally-expressed Sabino" theory to at least some question. Kind of fascinating, whatever the result. Montanabw 23:16, 11 October 2006 (UTC)

I have never come across a site, paper or expert in the field that has stated or implied that the so-called Lethal Albinism is not Lethal White Syndrome. Could you please state your sources. Thanks. Diamond Phoenix 02:24, 12 October 2006 (UTC)

UC Davis, for one: http://www.vgl.ucdavis.edu/~lvmillon/coatcolor/coatclr3.html

http://www.vgl.ucdavis.edu/~lvmillon/coatcolor/fig1a.html and

http://www.vgl.ucdavis.edu/~lvmillon/coats.html

VetGen (a competitor to Animal Genetics) for another:

http://www.vetgen.com/equinecc.html

"In the presence of the dominant allele W, a horse from birth will typically lack pigment in skin and hair. The skin is pink, the eyes brown (sometimes blue), and the hair white. Sometimes such a horse is called albino. The W allele is only rarely encountered. All non-white horses are ww. The homozygous condition (WW) is lethal"

The piece from the Blackwell Synergy site is abstracted from a peer-reviewed journal, Journal of Animal Breeding and Genetics

Volume 121 Page 374 - December 2004

doi:10.1111/j.1439-0388.2004.00481.x

Volume 121 Issue 6

Hence, my take is that this article by Swiss researchers is every bit as good a source as anything else on Wikipedia, and from the abstract, they seem to understand that W is a "real" gene and is not the Sabino gene, though they were curious if the two were linked. As for citation, it is a 2004 piece, it takes awhile for others to jump in and write something that needs citation, especially in this field.

(Given that "dominant white" appears to cause prenatal death, whereas LWS foals usually die after being born, there is a significant difference there)

Bottom line for me is that there is no link (yet) to lethal white linked to Sabino, SB1 has been identified as a separate gene (though there may be others) and in breeds with Sabino but not the O or N Overo or LWS gene, such as Arabians, Tenessee Walkers, Clydesdales, etc., they don't have lethal white (though Arabians have a weird thing called Lavendar Foal Syndrome, which may be linked to some kind of dilution activity, as most dead foals have a diluted coat color, hence the name).

The theory of dominant white not existing or not being lethal in homozygous form (WW) has yet to be "disproven," and as recently as 2004 seems to be still in the mix. I would be interested in seeing sources from peer-reviewed literature that say it doesn't exist. Hard to prove a negative, I suppose. Montanabw 23:11, 24 October 2006 (UTC)

Your sources only state that homogenous W is lethal, they do not say that the condition is different to that of Lethal White Overo. This is nothing new, and by no means implies the two conditions are sepparate.

I am yet to see anything suggesting Lethal White Syndrome is linked to Sabino. My statement was merely saying that from what I read of the article, it seemed they had mistaken the effect of the sabino gene (as far as colour is concerned) for the effect of the W gene, and it is possible they had merely mapped the sabino gene, not the W gene.

As for the article I referred to, perhaps it is a little soon to be drawing conclusions about it. Although it is unusual for an article to go this long without citations, it does not necessarily mean that this is due to poor conclusions. I therefore retract my statement suggesting as such.

And in reference to a statement you made a while ago regarding the editing of the article: "My point is merely that we float test balloons before diving in with wholesale edits of what clearly was an article that someone took a LOT of work to create." I can understand how you can feel some sort of attachment to an article you put a lot of effort into, but I do not see this as an excuse to leave inaccurate data available to the public purely for sentimental reasons. In the equine genetics inductry, new discoveries are being made all the time, so naturally, new information will have to be added to update the article, and disproven theories will have to be removed. It should also be noted that my purpose to update this article does not include revamping the entire thing, merely stating the different theories, be they true, false, or disputed, and discussing why they have such a status. You will not lose much of your work, unless it is merely repeating something that I will say in a more concise manner. I will be happy to discuss with you any ideas for improving the layout and content of this article.Diamond Phoenix 13:14, 26 October 2006 (UTC)

I'm not a contributor on this article other than to wikify some links and tweak some grammar. I have no emotional attachment here. My point is simply that SOMEONE went to a lot of work, and while you offer criticisms, I guess it would be more valuable if you offered more specific sources that can correct any specific errors you see in the article. That or create a separate article or project (call it "21st century equine coat color genetics or something) where you can put in your material and then link it to this discussion page so those of us who care can maybe see it evolves into something that can be merged into the current article.

and

The W gene that can cause lethal albinism does not appear to be the same as the one mapped Sabino gene, SB1. It also isn't the same as the "O" gene (using UC Davis designation) that causes LWS. Lethal White and Lethal albinism are two different conditions, apparently caused by separate genes. Sabino appears to have NO connection to either condition--Sabino exists in Arabians, for example, but not the other two, and Arabians, though they have other genetic lethals like SCID, there is no documented case of any type of lethal white in Arabians. The way I see it, the W gene has been discussed in research literature for decades and I haven't seen a source that effectively argues that it doesn't really exist...though if one exists, I'm all ears. Montanabw 05:14, 27 October 2006 (UTC)

I think you misunderstood what I said. From what I can tell, it seems the researchers have mistaken Maximum Sabino horses for Albino horses (based solely on the fact that they are all completely white). It has long been accepted that these two genes are sepparate from each other, and I don't dispute that. However, I find it interesting that in reference to the horses they studied, they state:

"It seems, that the action of the dominant white allele is not always fully penetrant, resulting occasionally in spotted look alike offspring. These horses resemble a coat colour pattern known as sabino spotting."

"All of these white born horses transmitted the white or almost white phenotype in a dominant manner to their progeny." (Note: most Maximum Sabino horses are almost completely white.)

"Among solid coat colours, dominant white (W) segregates in this light draft horse population, going back to a founder mare ('Cigale') born in 1957. According to the studbook entries, the parents of the white-born founder mare were both of solid pigmented bay coat colour, with only negligible white markings." (Note: a single sabino gene results in white markings on the face and/or legs, and could quite likely be overlooked, resulting in the horse being recorded as solid.)

"All horses were classified into two categories as either solid coloured or dominant white; the latter including also 'sabino-like spotted phenotypes'. Thus, in this study, all horses observed with the sabino-like colour pattern were treated as incomplete dominant whites." (Since the Sabino gene has already been mapped, it is clearly not Dominant White, yet in this study it seems it has been treated as such.)

"White horses carry mostly tiny residual pigmented patches and have sometimes even 'spotted', sabino look alike, offspring (Fig. 2). These 'spotted' look alike horses may again have entirely white progeny." (This is consistant with the Sabino gene inheritance.)

"Microsatellite ASB23 was not fully informative in the pedigree, as some dominant white horses (W/w) were found homozygous for one of the marker alleles." (Note: Homogenous Sabino causes Maximum Sabino.)

"In addition, a focus should be given to an accurate description of phenotype nomenclature, i.e. to the question of whether dominant white is in fact an exhaustive expression of the sabino colour pattern or the sabino phenotype the result of incomplete penetrance of dominant white?"

All of these statements can easily be explained with reference to sabino gene(s), not W. In their conclusion, the researchers all but state this (see last quote) when discussing possible future research.

Their examinations of pedigrees and offspring of the tested horses suggests evidence of Sabino patterns, but their data is mentioned vaguely, so I cannot give a definite yay or nay on this theory. The lethal nature of the genes they mapped were not studied. It was assumed all horses tested were W/w. Their evidence suggests otherwise (see the second-to-last quote), which suggests that either W/W is not lethal, or that they were not looking at W genes. Unless the horses can be shown to NOT have a non-albino condition that causes the horse to appear completely white, it cannot be concluded that the gene they mapped is actually W. You might be interested to note that the W gene the researchers refer to is consistantly given the name 'Dominant White'.

Also, I am still working on the equine genetics article I am writing. It is nothing more than a summary of all known theories in this area, so it should be appropriate for Wikipedia. It is not finished yet, because I still have to summarise the pattern genes, and the most recent discoveries and conclusions (those that have come out since I started writing it), but it should be finished soon. I will add it to the wikipedia entry once I am done, including all my sources and references. It should be noted, however, that many of them are not online. Be patient and I will get this up soon.Diamond Phoenix 08:50, 27 October 2006 (UTC)

Cite your source, please. I'm not even sure what point you are trying to make here.Montanabw 03:24, 29 October 2006 (UTC)

Cite my sources? I already did! If you're going to respond to a comment here, please read the WHOLE thing. I don't like to repeat myself. The paper is the same one I was referring to at the beginning of this section (White genes). I even provided the link. Unfortuanately, only the abstract is available to the general public. The quotes I mentioned were taken from the body of the article. As for the point I was trying to make - I was trying to emphasize the poor quality research these people had undertaken, more specifically the number of possibly incorrect assumptions they had made, such as a horse that appeared sabino actually being albino. Diamond Phoenix 05:09, 30 October 2006 (UTC)

As for "it seems the researchers have mistaken Maximum Sabino horses for Albino horses" I only want to note that there is NO SUCH THING as an "albino" horse, i.e. with red eyes, etc...they die in the womb, and best evidence I have is it's because of WW. I also understand LWS to be affiliated with homozygous Frame Overo gene (OO), and that "lethal albino" (WW) is NOT LWS, (OO). I was under the impression that some people claim that there is no "W" gene at all and that all "White" horses are maximum sabinos, an assertion that I don't buy. Not sure if that is your position. There might be such a thing as a "Maximum Sabino," though I would like to see the evidence for that. I suppose there could be "maximum Tobiano" horses too--after all, isn't "maximally expressed" basically the state of the horse being one big spot??

I sort of buy the idea that sabino is a gene-complex and may come from multiple sources...while there have been true white Tennessee Walkers, they can also produce Pinto coloring. But, I have NEVER EVER heard of a "true" white Arabian (all "white" Arabians are actually grays) nor a "true" white Clydesdale, and both carry a type of Sabino gene, but neither of which ever carry any other Pinto patterns. My points are simple: 1) The source-citing thing needs to be all around who are the genetics gurus you feel have superceded the work of Bowling and Spooneberg? 2) there's no such thing as a living "real" Albino horse, no matter how you look at it,they die, and 3) If there is such a thing as a "Maximum Sabino," then there must be more than one gene responsible for Sabino coloring, because "maximum Sabino" never occurs in at leasty two breeds who have Sabino markings. Montanabw 03:24, 29 October 2006 (UTC)

Again with the misquotes! "As for "it seems the researchers have mistaken Maximum Sabino horses for Albino horses" I only want to note that there is NO SUCH THING as an "albino" horse" What I was trying to say is that it seems the researchers see a Maximum Sabino horse, and think its an Albino horse. These researchers are not only trying to prove the albino gene exists, but also map it. You also seem to be unfamiliar with the whole White theory: WW=lethal albino, Ww=albino (carrier of lethal gene), ww=non-albino. According to Sponenberg or Bowling. By this theory an albino should be able to exist. In practice I've never seen conclusive evidence of the gene existing, but thats beside the point. Also, you keep stating that Lethal Albino and LWS are two different things, yet you never quote an expert saying as such! You might also be interested to know that not all albinos have red eyes, regardless of animal species. In many cases the eyes are blue. Other possibilities might exist. Typically, though, albinos have white hair/fur/etc, and pink skin (if applicable). A horse with the sabino gene tends to have pink skin, blue eyes (very rarely brown), and white hair on at least part of its body. So its not so unusual to think that a Maximum Sabino might be mistaken for an albino. (Technically speaking, Sabino, along with the other pattern genes, is a type of localised albinism, but not THE albinism that is supposedly caused by the W gene.)

I'm not sure where you're getting your information on sabino, but you're way out. For the sabino 1 locus, at least, one sabino gene results in sabino markings on the face, legs and occasionally belly, while two genes results in fully expressed sabino, ie: Maximum Sabino, where most or all of the horse is white. A second sabino gene is theorised to exist, but I don't know how it is supposed to act. I think the Sabino 1 gene has a genetics test for it now, so the sabino theory stated here has been conclusively proven.

As for Maximum Tobianos (ToTo?) these don't exist simply because the Tobiano gene acts in a different way to the known Sabino gene. Maximum Tovero can exist, but this is several different genes, eg: Spl, Sa, To, all acting at once to create a white or near-white horse.

I hate to say it, but your knowledge of the actions of the pattern genes seems to be pretty poor. Next time, instead of questioning my knowledge on the subject, look it up, either here or elsewhere, to find out what the generally accepted or plausible theory(s) are, THEN come discuss it with me if you feel it necessary. I'm sorry, but I really see no point in debating such easily accessible, proven information.

Whoa, calm down! I am far from "way off." In fact, I am simply raising some of the same questions about your evidence, knowledge and research that you are raising about mine. (and I really question if a group of researchers are so stupid as to confuse albinos and maximum sabinos! I really doubt it.) Most of what I get is from UC Davis, though I have looked at some other source material, including the frame overo "L' versus "O" gene controversy over LWS that resulted in the independent research at U Minn, and some of the stuff out of U Virginia as well. Bowling says WW is lethal albino. (see below)

The SB1 gene has been mapped, and it may be maximum sabino when homozygous, but sabino coloring seems to be produced by a gene complex or by different genes--some forms of Sabino absolutely, positively cannot act like SB1 does. If Sabino coloring always produced a white horse when maximally expressed in homozygous form, then there would be true white Arabians, and I guarantee you that there is absolutely, positively no such thing as a white Arabian (all "white" Arabians are actually grays). Some purebred Arabians carry Sabino patterning, but NEVER have pink skin (except under white markings), or blue eyes, ever. I do not believe that there are any "white" Clyesdales, either. UC Davis says "A mutation has recently been discovered that produces one type of sabino pattern. It has been named Sabino1 as it is not present in all sabino-patterned horses...Sabino1 is most commonly found in Tennessee Walking Horses. Other breeds in which this mutation has been found include: American Miniature Horses, American Paint Horses, Aztecas, Missouri Foxtrotters, Shetland Ponies, Spanish Mustangs and Pony of the Americas. Other breeds of horses that are known to have sabino patterns, such as Clydesdales and Arabians, have so far tested negative for the Sabino1 mutation, although the number of animals tested is low." http://www.vgl.ucdavis.edu/service/horse/coatcolor.html#sabino1

Here's some of my source material on albinism:

In horses, the white or "W" gene is known to be responsible for the absence of pigment which is usually referred to as albinism. Bowling, Ann. "Coat Color Genetics: Positive Horse Identification." The theory that "dominant white" is lethal in horses--when the W gene is homozygous (WW)--was first proposed as a theory in 1953 and after 15 years of test breeding, was confirmed in 1969. Householder, D. Douglas. [http://animalscience.tamu.edu/ansc/publications/horsepubs/hrg003_coatcolor.pdf "The Genetics of Equine Coat Color" Texas A&M University Department of Animal Science Equine Sciences Program, publication HRG-003 (undated). The same group of researchers found that the WW gene complex was also lethal in Dexter cattle, platinum foxes, and bluefrost minks. See also the full cite of the blackwell article is, I think: Mau, C., Poncet, P. A., Bucher, B., Stranzinger, G. & Rieder, S. (2004) "Genetic mapping of dominant white (W), a homozygous lethal condition in the horse (Equus caballus)." Journal of Animal Breeding and Genetics 121 (6), 374-383. doi: 10.1111/ j.1439-0388.2004.00481.x. Accessed September 6, 2006 at [1

So please, understand that you may not have the full picture here, either, assume good faith and realize that other people research this issue as well. I don't breed for spots, so I don't even really know why I am spending all this time arguing about it, I actually have no axe to grind other than figuring out the truth. Montanabw 05:53, 1 November 2006 (UTC)

"and I really question if a group of researchers are so stupid as to confuse albinos and maximum sabinos! I really doubt it." Is it really that hard to imagine? Maximum sabinos and 'albinos' both have all-white hair, pale eyes, and pink skin. In the case of the former some small amounts of spotting can occur, but not always. The quotes I mentioned above have been taken from the article by these researchers, and they clearly state that any horse that appeared sabino was recorded as albino.

Evidence exists to say that there is at least two genes that cause sabino spotting (currently named sabino 1 and sabino 2). I do not dispute such a claim. I've got an email somewhere from one of the current genetics experts that goes into this in detail. I'll try to find it. Also, I might have been mistaken when I stated that homogenous sabino 1 caused maximum sabino. I was quoting from the theory that came about before knowledge of sabino 2. All that is really clear, from what I know, is that more sabino genes are needed for maximum sabino, than for 'normal' sabino. Diamond Phoenix 04:06, 2 November 2006 (UTC)

SB1 is the gene that might be responsible for maximum sabino, according to UC Davis, from what I understand, and as I just stated above, SB1 has not ever been found in Arabians or Clydesdales, which makes sense, because they are never "white." I have seen no evidence for only two sabino genes, I think I agree that they don't know for sure all the ways Sabino occurs, but one gene so far has been mapped.

Here's my question about this whole thing: Are you asserting that there is no such thing as the W gene? Are you asserting that ALL "albino" or "white" horses are maximally expressed Sabinos? I don't want to misunderstand your position here... Montanabw 23:05, 2 November 2006 (UTC)

I'm saying there is no conclusive evidence to suggest that the White gene even exists. I don't know what causes the effect that is described as albino, but I certainly think sabino is a good possibility, although not necessarily the only one.

I know you stated earlier something about test breeding, but it should be noted that this sort of proof does not confirm the existance of White, only suggest it exists. Something similar occurred regarding Lethal Roan. Not long after the Lethal Roan theory came about, test breeding was undertaken, with the conclusion being that several healthy homogenous roans were seen. It is now thought that roan might be polygenic, in which case previous test breeding would be inconclusive, and it is now though Lethal Roan might be a possibility. Diamond Phoenix 12:05, 3 November 2006 (UTC)

I've heard the theory that the W allele doesn't exist, but W has been discussed in peer-reviewed literature for decades, the theory is still on the UC Davis web site, and the symptoms of lethal albino sound different from Lethal White Syndrome-- and LWS is linked to Frame overo, not to sabino anyway, so I guess I would like to see whatever articles are out there saying the W allele doesn't exist...though hard to prove a negative, I suppose. I just don't buy the "all white horses are maximum Sabino" theory. If you have some sources I can look up myself, do provide them here. Otherwise, I am getting tired of this issue and shall await whatever appropriate edits may be made to the article. ThanksMontanabw 17:57, 3 November 2006 (UTC)

Try looking at the evidence FOR white genes. Especially some of the first evidence by (I think) Sponenberg that made him suggest the White gene in the first place. Its very shakey. (In case you can't find it, he basically states that a lot of horses appear completely white, and names the gene that causes this as dominant W -the first mention of W, I might add- then also notices that a lot of foals that are born completely white end up dying due to a colon defect, and makes the assumption that the gene that causes the foals to be white is the same one that causes the other white horses to be white. -Interpret this how you will-) The problem with many of the methods that look at the White gene is that they identify the presence of albinism solely on the colour of the horse. As i've mentioned, phenotypically, albino and maximum sabino are often identicle. According to theory they are genotypically different, but that remains to be proven. As for the differences between LWS and lethal albino, you keep stating that the symptoms are different, yet never do you state a source for it (despite my repeated requests for it), and never have I so much as heard of an expert implying this. For the last time, PLEASE STATE YOUR SOURCES!!! User:Diamond Phoenix 11:46, 6 November 2006 (UTC)

Um, I did, above, but I'll give you a list again...the same list:

http://www.vgl.ucdavis.edu/~lvmillon/coatcolor/coatclr3.html

http://www.vgl.ucdavis.edu/~lvmillon/coatcolor/fig1a.html and

http://www.vgl.ucdavis.edu/~lvmillon/coats.html

http://www.vetgen.com/equinecc.html

and

"Coat Color Genetics: Positive Horse Identification." The theory that "dominant white" is lethal in horses--when the W gene is homozygous (WW)--was first proposed as a theory in 1953 and after 15 years of test breeding, was confirmed in 1969. Householder, D. Douglas. [http://animalscience.tamu.edu/ansc/publications/horsepubs/hrg003_coatcolor.pdf "The Genetics of Equine Coat Color" Texas A&M University Department of Animal Science Equine Sciences Program, publication HRG-003 (undated). The same group of researchers found that the WW gene complex was also lethal in Dexter cattle, platinum foxes, and bluefrost minks.

And for the last time, THERE IS NO SUCH THING AS AN ALBINO (living) HORSE. "Albino" terminology is outdated. I don't think you actually read what I wrote here. The colon defect is LWS, versus lethal albino foals who die en utero ...and Sabino appears to have NEITHER lethal albino or LWS (this is a good thing). And, frankly, Sponenberg was far from the first to propose the W gene, and the late Ann Bowling had pretty impressive credentials and wrote a textbook on the topic, so until I hear something quite convincing, I'm sticking with them. Now back atcha...where is your source that W doesn't exist? List it in full here so I can look it up myself. Montanabw 09:24, 6 November 2006 (UTC)

I DID read what you wrote. Perhaps you missed my reply. I'll state it again to save you the trouble of looking for it: those sources only state the theory of the white genes. Not once do they say the symptoms of it are different to those of LWS. In fact, they don't even detail what the symptoms are. I'm not even sure you've read your own sources. They have almost no relavance to what you are stating.

You also say that there is no such thing as an albino horse. Although this is pretty much what I've been trying to say all along, it suggests that you are not familiar with the White theory. On the same sites you list above, it says that a single (dominant) white gene results in an "albino" horse (yes, they do use that terminology), while two of them is lethal. Now lets leave the dispute about teminology out of this, and just stick to the subject of the argument.

Finally, you state that sabino has neither lethal albino or LWS. I agree with you on this point, but I think you misunderstood what I said earlier. I was trying to say that Sabino horses are sometimes identified as albino based only on their phenotype (what they look like). Other factors are not looked at to determine if they have LWS or lethal albino or nothing, so there is nothing to suggest that the horse is not albino. If other factors WERE looked at, then it would be clear whether or not the solid white horse in question was sabino or albino or something else.

As for stating my sources, if I have them on hand I do try to post a link to them. Unfortunately, a lot of my sources are not found on the internet, eg: email/verbal conversations, so backing it up with physical evidence is not always possible, unless you want names and addresses so you can research it and contact the people yourself. Some sources aren't in English either, which is clearly a problem. Another problem is the great quantity of sources. Sifting through them all to find out which ones I'm quoting is not always practical. Especially when I am quoting from a conversation - i've simply talked to too many people to know who said what. Once I post all my data on here I'll include ALL sources though, so you've welcome to sift through it all then, and critically analyse the validity of them. Diamond Phoenix 12:26, 6 November 2006 (UTC)

"Albino," referring to a living white horse with the W gene, is an outmoded and incorrect term, whoever is using it, though I suppose it's a handy, if careless shorthand. The American Albino Registry even changed its name to reflect the reality that there are no true albinos in the horse world. (i.e. pink eyes) Beyond that, I shall eagerly await your results. It will be explosive and revolutionary to have both Bowling and Sponeberg proven wrong by a lay person such as yourself. I can't wait. Montanabw 18:33, 6 November 2006 (UTC)

Let's keep it civil shall we? There's no need for sarcasm.

My reason for stating that W does not exist comes from real sources, not things I've made up, or attempted to directly research myself. A while ago I posted on a forum the article I wrote, that I've previously mentioned. It can be found here: http://hababeri.com/erworld/index.php?topic=6002.0 This particular version of my article is incomplete and a bit old, and my knowledge of horse genetics has since improved, plus new discoveries have been made, resulting in the accuracy of some sections being a little less than perfect, but most of it should be reasonable. More importantly, it also includes all the sources I used, and a glossary of terms. Anything I have said can be backed up by the sources listed here. Some are people, not sites, so you won't necessarily be able to find them all on the internet, but you might be able to find an email address if you wish to contact them. My article does not go into a lot of detail on the White gene theories, but my sources will, if you care to look them up.

And for future reference, in animals in general, 'true albinism' does not necessarily result in pink eyes. Animals can still be correctly classed as albino without having pink/red eyes. Just google 'albinism' if you don't believe me.

Genetics News

Some exciting discoveries within the past month... Two new genetics test are now available. One is for the silver dapple gene, but the other is for a rare, newly discovered gene known as Pearl (aka Barlink). This gene seems to act in a very complex manner, depending on the presence of the creme gene or homogenous chestnut. I'll try to get my hands on the official article... Diamond Phoenix 13:14, 26 October 2006 (UTC)

Interesting and way cool...what University or lab? FYI, Equus Magazine this month ran a fascinating article on Brindle coloring in horses, which is extremely rare, and may possibility be linked to chimerism, of all things--the horse literally having two sets of DNA. Very interesting. Montanabw 05:27, 27 October 2006 (UTC)

The generally accepted theory is that Brindle is as a result of chimerism. This is not a new theory, although it is possible their evidence for it might be. Still, I'd appreciate it if you could post a link for this article. It does sound fascinating. Diamond Phoenix 08:55, 27 October 2006 (UTC)

Maybe not new in other animals, they say male tortiseshell cats are "often" chameric. But it's brand new to horses...According to the article in Equus, the Quarter Horse stallion Dunbar's Gold was the FIRST horse ever identified as a Chimera. "Horses of a Different Stripe" Equus,, Nov. 2006 p. 21. Have print copy, not sure if they post this month's issue online yet, but it's still on the newsstands, I think. Neither Sponenberg, who was consulted for the article, nor Cecelia Penedo, Bowling's successor at UC Davis, had ever ran into these before. They have been under the impression that Brindle was caused by a modifier, but this is making people rethink it--maybe not all brindled horses are chimeric, but apparently it is possible that all chimeric horses are brindled. Fascinating no matter what. Montanabw 04:03, 29 October 2006 (UTC)

Just because the two main experts in the field have not come across this before does not mean that it is a new theory. When I was researching brindle in horses, I came across plenty of sites that stated it was chimerism, although admittedly I don't know how much proof they had for it. These people may have prooven that brindle is chimeric, but the theory for it is not recent. Off the top of my head, I can't quote any sources, but if you look it up on google, it should be fairly simple to find. Its actually quite common, as these things go. Diamond Phoenix 02:13, 30 October 2006 (UTC)

The pearl gene info can be found at http://www.vgl.ucdavis.edu/service/horse/coatcolor.html

I wouldn't say "plenty" or "generally accepted theory," but I'll grant you it isn't a brand new theory--just brand new evidence. Looks like the best set of links to older info on brindling appears to be here <http://www.geocities.com/sbatteate/>, but the earliest article with the chimerism theory seems to be from '99, and the evidence didn't look too strong, more an educated guess by the author. However, what we have in the 2006 article are the first horse chimeras CONFIRMED by DNA testing. See also <http://members.aol.com/brindlehos/> Sounds like the Quarter Horse Journal scooped Equus by about nine months. "Extremely rare, chimmerism has been documented in other species, and is now documented in Horses as a result of the work at UC Davis. Dr. Cecilia Penedo also presented her findings at The Horse Genome Mapping Workshop that was held on Aug. 22 in Port Seguro, Brazil." Montanabw 05:49, 1 November 2006 (UTC)

Just for interest, there is a rare pattern known as white brindle. This appears to be the same as brindle, but with white stripes, rather than black. The current theory states that this is as a result of chimerism with the roan gene. Just a curiosity - i don't know how accurate this theory is, or what evidence it has. Diamond Phoenix 04:06, 2 November 2006 (UTC)

End of White discussion?

The best article I have seen on the white gene issue is Overton, Rebecca. "By a Hair" Paint Horse Journal March 2004. It explains LWS and how that test works, it mentions W as a gene that really does exist and says that WW foals are actually reabsorbed as embryos, it discusses the way the LWS gene cannot be determined by coat pattern, as it can be masked by many colors, it has even cropped up in the offspring of solid-colored horses. This one may be the most useful in practical terms. Now, can we end this discussion? It's getting redundant. User:Montanabw

Found the site for it: http://www.painthorsejournal.com/archives/index.html The article referred to here is the 3rd one from the top. Diamond Phoenix 12:29, 6 November 2006 (UTC)