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SEVEN more KIT mutations (Dominant White)

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accphotography
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Re: SEVEN more KIT mutations (Dominant White)

This is Deebrand (the mare, standing by Turf Club):

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Arabica
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Re: SEVEN more KIT mutations (Dominant White)

I wonder what the Argentinian TB stallion Royal Manchado might test as fas as DW is concerned or that Arabian mare Trabag.

http://www.pedigreequery.com/royal+manchado" onclick="window.open(this.href);return false;

accphotography
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Re: SEVEN more KIT mutations (Dominant White)

If it is truly environmental, it probably won't test as anything. Do you know if it has passed on? If so, I wonder what would happen if you moved one of the stallions or mares with the pattern out of the area and then bred them so the foals wouldn't' be exposed to the "environmental factor". It would be interesting to see if the foals would have the pattern or not. If they did, it probably is genetic somehow.

The thing that bugs me about it is that it has happened in numerous breeds in the same area. The chances of each of those breeds developing a mutation that is identical is very, very slim. That strongly points to environmental. Especially when it's never been seen out of that region.

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duncentralstation
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Re: SEVEN more KIT mutations (Dominant White)

I agree with you 100% on the environmental angle, ACC. If it has only been seen in a particular region, in various breeds of that region, and does not appear to be passing on to offspring, that does seem to indicate an environmental factor, rather than genetics.

Of course, I think that sometimes environmental factors can change the genetics, causing a mutation that can be passed on to offspring.

From the info included about Royal Manchado and the other horses in that region, it doesn't appear to have been passed on to offspring, though.

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CheyAut
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Re: SEVEN more KIT mutations (Dominant White)

For the embryonic lethal (homozygotes), at what stage in developement does this occure? Just curious :)

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accphotography
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Re: SEVEN more KIT mutations (Dominant White)

I don't think they know for sure as they haven't followed any matings. In fact I *think* (Nancy correct me of you know) the only reason they think it's a homozygous lethal is that they've yet to find a living homozygous, and obviously it would be embryonic as they're not having foals like LWOs. Based on the specific mutation information Nancy provided I feel it would be VERY early. Maybe they wouldn't even be viable. That's just my theory though.

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duncentralstation
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Re: SEVEN more KIT mutations (Dominant White)

For the embryonic lethal (homozygotes), at what stage in developement does this occure? Just curious :)

Because these mutations are so rare in horses, I don't think anyone knows the answer to this question. Breeding trials would have to be performed, which would involve getting permission from an ethics committee to do "animal experiments".

Or, breeders would have to do their own "experiments", which would involve inbreeding because each mutation is unique to its family line, as well as constant monitoring of each possible homozygous pregnancy via ultrasound to track the embryo and document at what stage of gestation its death occurs.

I'm sure this has been studied in mice, for example, already, which would be how they would know that these types of KIT mutations are usually embyonic lethal when homozygous.

ACC ... My guess would be that it is an early embryonic death, too, but that's just a guess on my part.
As far as I understand, there are a number of reasons they predict the W mutations in horses to be embryonic lethal when homozygous, one reason being what is known and has already been found in mice and pigs that were found to have W mutations. My guess is that they have been able to study these species more closely, perhaps have been able to do breeding trials (at least with mice?) with them in the past?? Don't know about this for sure.

And because they have been able to study mice and pigs with W mutations in the past, they have known for quite some time that KIT is responsible for the development of important functions other than skin and hair pigmentation (development of mast cells, for example), and based on what has already been found in other species with W type mutations of KIT, whenever they see a mutation of KIT that would produce very, very little KIT protein when homozyous, its probably a fairly safe prediction that homozygotes are likely embryonic lethal.

So it is based on the science as studied in other species so far, and really not based on a lack of having found any "WW" horses living. The lack of any "WW" horses being identified at this point may only mean ...

1) .... that no "W" horses have been bred to other "W" horses of that family/breed because they are too closely related, thus there are no horses of that particular family/breed that could even possibly be "WW".

Or ....

2) .... that if some inbreeding or close line-breeding has been practiced in any of the W breeds, so far a homozygote has either not been produced, or has not been identified/confirmed.

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accphotography
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Re: SEVEN more KIT mutations (Dominant White)

That makes more sense. Thanks.

Albeit in the original W article they did point the finger at not having found any WWs.

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duncentralstation
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Re: SEVEN more KIT mutations (Dominant White)

Right, they had not and still have not found an horses that have tested homozygous for these mutations. Obviously, if they had found even one within any given mutation, the specific mutation would likely have been called a sabino mutation, rather than a (Dominant) White mutation.

The lack of any "WW" horses is just one part of the equation for predicting embryonic lethal, though. Science plays a huge role, because they know that in other species, these same types of mutations of KIT do result in embryonic lethal, and they know this is because not enough KIT protein is produced when in homozygous form. Hence, it is reasonable to predict the same would be true of similar types of mutations of the equine KIT gene as well.

This may not be well described (if at all) in the original study, I know. It is mentioned to some degree in the latest study, plus I had picked the researchers' brains some time ago about why Dominant White rather than Sabino (like the Sabino 1 mutation), as I knew of a number of folks who were ... shall we say ... less than pleased with some of these mutations being deemed "Dominant White" instead of maximum sabino. I wanted to hear directly from the researchers how it was determined that these were Dominant White vs. Sabino.

The simplest explanation is that Sabino mutations can exist in homozygous form, Dominant White mutations are (proven to be, or predicted to be) embryonic lethal. And I want to clarify that "predicted to be" means that based on scientific evidence as discovered in other species, it can be reasonably predicted to be embryonic lethal. In this case it is scientifically known from studies in other species that insufficient production of KIT protein results in embryonic death, therefore the same is predicted to be true in horses at this time.

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CheyAut
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Re: SEVEN more KIT mutations (Dominant White)

That makes sense. Thanks! :)

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nerd
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Re: SEVEN more KIT mutations (Dominant White)

Resurrecting this old thread,
Re: the identity of W7

I also cast my vote for Turf Club and Deebrand being the two individuals tested in the 'TB3' family where they defined W7.
My reasons for this are as follows:[list]
-birth year of Turf Club (2005) matches 'founder birth date' of W7 in Table 1
-Turf Club looks a whole lot like the horse in Figure 1.f
-in the supplemental info, the pedigree of TB family 3 is mostly consistent with Turf Club's (both are fillies, both have 9 siblings (listed on pedigreequery), the only inconsistency is that the pedigree in the supplemental info lists different sires for all the progeny whereas according to pedigreequery they are not all different)[/list:u]
Reasons against this are as follows:[list]
-Deebrand's other foal, Adorable, looks like she could be DW, which would be inconsistent with Deebrand being negative for W7 (however, if Adorable were W7/+, Deebrand's negative result could be explained if she were a mosaic/chimera of some sort)
-ACC, you mentioned that some of Deebrand's other foals had produced colored foals--who are they? The only one I can find (through pedigreequery, so by no means complete) is Adorable's Sato foal (this is essentially the exact same point as above)[/list:u]

Now, who is W6?
According to the paper it's a 2004 colt (the supplemental info shows no siblings)
The only 2004 cropout white TB I can think of is the Legal Opinion x Theresa's Delight filly, but the gender isn't right. Does anyone know of any others?

One possible hint as to the identities of TB2/TB4/TB5 is that the paper's Acknowledgements section contains the following:

The authors would like to thank Toshio Matsuda and Yanagi Sports Co., Ltd. for providing samples and pictures of white horses in Japan, and also appreciate the help of Kei-ichi Hirota and Mitsuo Fukunaga in the Laboratory of Racing Chemistry (LRC), and owners, trainers and staff of the Japan Racing Association (JRA) and National Association of Racing (NAR) for collecting samples in Japan

... which would seem to indicate that some of the unidentified TB families might be in Japan (but none of them look like Shirayukihime)
Any guesses?

accphotography
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Re: SEVEN more KIT mutations (Dominant White)

The Shira horse is all white so how could you tell?

I'll delve into this tomorrow when I'm not so tired. I have some things to add.

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nerd
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Re: SEVEN more KIT mutations (Dominant White)

I meant that none of the pedigrees look like Shirayukihime's

accphotography
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Re: SEVEN more KIT mutations (Dominant White)

Oh gotcha.

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colorfan
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Re: SEVEN more KIT mutations (Dominant White)

Could someone explain the significance of these mutations please?

I remember hearing that two overos shouldn't be bred together because of the lethal white gene.
Is that part of it?

Does this mean that a pinto pattern can be identified now by blood typing?

In this structure what is the meaning of dominant? Takes precedent over other colors?

I have been reading all evening, everything is starting to swirl :BH

When I went to the link in the first post I couldn't find an article only a paragraph summary.

What am I missing?

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accphotography
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Re: SEVEN more KIT mutations (Dominant White)

The full article may not be available any longer, I'm not sure. I read it at one point so it was out there.

No, it's not really the same. Two FRAME overos shouldn't be bred together as they could produce a lethal white foal that dies shortly after birth. Dominant whites that are bred together have a chance of producing a homozygous embryo that is not viable, meaning it never really implants (suspected mind you) and thus many people may think the mare just "didn't catch". LWO/Frame overo is the only gene that results in a foal that dies shortly after birth.

At least four distinct pinto patterns can be identified by genetic (using hair) testing. Tobiano, frame overo, sabino1, and 11 dominant whites.

Dominant means it only takes one copy to express. A heterozygote will show full expression of the gene.

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Daylene Alford
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Re: SEVEN more KIT mutations (Dominant White)

LWO/Frame overo is the only gene that results in a foal that dies shortly after birth

Actually this isn't true. There is lavender foal syndrome in Arabians and may be others of which I'm not aware. It is true as far as white patterns are concerned.

accphotography
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Re: SEVEN more KIT mutations (Dominant White)

I meant in the white patterns... but that is confusing anyway. I'm not sure I knew that's what LFS was. Good to know, thanks!

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Daylene Alford
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Re: SEVEN more KIT mutations (Dominant White)

I don't know much about LFS either. Just that it results in a diluted foal that dies shortly after birth.

I think I'll start a thread about this. Its been a while since I've seen anything on it and would like to know more.

colorfan
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Re: SEVEN more KIT mutations (Dominant White)

When you say sabino1 does that mean sabino has sub categories?

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lillith
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Re: SEVEN more KIT mutations (Dominant White)

Only one mutation for sabino has been mapped and has a test avaliable atm, Sb1. However there are a lot of sabino looking horses out there who test neg to Sb1 so it is hypothesised that there are a fair few more sabino genes out there, hence naming the first one 1 so the next one found can be dalled Sb2 and so on.

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Maigray
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Re: SEVEN more KIT mutations (Dominant White)

To make matters even more confusing, the dominant white phenotype looks exactly the same as sabino.

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