7 new mutations in KIT found, including two more TB DW!!

[RiddleMeThis]

Ok, but this contradicts everything I've ever read about Roan. Including the breeders who have been seeing a 1:3 ratio instead of a 1:2:1 ratio in roan x roan matings. Roan has kind of been the poster child of early embryonic lethals.


And what they are testing is markers, not the actual roan mutation. If there was a mutation to the roan mutation, it follows that most of the markers would be the same. And until someone finds the actual mutation, there's no telling just how many versions of roan may be out there. DW is up to how many now?


And yes, I could have gone intro the bio-geek speak and talk about Exons and the like, but was trying to provide a over view of how it works to someone that is not a native English speaker, hence the simplifications and examples with roan.

The only thing Ill say to that is that the researchers at UC Davis FIRMLY believe that their is only one Roan mutation in the majority of horses and that it is NOT homozygous embryonic lethal. There are plenty of horses not only TESTING homozygous but PRODUCING. The horse those test results are from is currently 21 for 21 with Roan.

And there are QH roans that have in the triple digits of Roan offspring with none being non roan.

[Shannon]

Isn't the 50/50 rule a theory more than actual norm? Like grays? And the more offspring the more likely to see a closer ratio.
I vaguley recall doing some experiments with fruit flies in university...

[RiddleMeThis]

Isn't the 50/50 rule a theory more than actual norm? Like grays? And the more offspring the more likely to see a closer ratio.
I vaguley recall doing some experiments with fruit flies in university...

50/50 is what it would be in a perfect world and it does get VERY close to that and clsoer and closer and closer as the numbers go up and up. Which is why its best to use large samples when figuring out zygosity without tests. (which is also why I brought up the triple digit foals that are roan with none being non roan.)

[xfactor fan]

http://www.springerlink.com/content/42079uyy8vprhw7a/

Abstract
The roan coat color in horses is controlled by a dominant allele that is lethal in the homozygous condition. Phenotypic similarities to some pigmentation disorders in human and mouse, combined with comparative mapping data, identified KIT, encoding the mast cell growth factor receptor, as a major candidate gene for the roan locus (Rn).

First sentence from the article. This has pretty much been the majority view for a long time.

Don't know what the UC Davis folks are looking at. There may be several types of roans, Some may be lethal, some may not. Genetics is evolving so fast it is hard to keep up with all the developments.

When A. Bowling came up with the study that proved there were some Homozygous roan there was a great outcry. There's a pretty nice article on roans here:
http://www.hancockhorses.com/article-roan.html

The solution that fits observed facts seems to be at least two versions of the Rn gene. Rn1, and Rn2. with the Rn1 -Rn2 not being lethal. The Hancock Roan article does mention that there are a large numbers of barren mares, and late foals which would be consistent with a mixed breeding population containing Rn1 and Rn2.
So the herd would have Rn1 rn, Rn2 rn, and Rn1-Rn2 members.

Only the Rn1-Rn1, and the Rn2-Rn2 embryos would be lethal.



Most of this will settle out when someone finally finds the actual Rn mutation

[RiddleMeThis]

Don't know what the UC Davis folks are looking at.

UC Davis folks are looking at their OWN research. And considering the article you linked is about 12-13 years old, I will go with the most current research.

[Linda_d]

Before the AQHA accepted cremellos and other double dilutes, and when many breeders thought palomino-to-palomino matings produced "albinos" (actually cremellos), very few AQHA breeders would intentionally breed palominos to palominos because they didn't want unregisterable foals.

I think the roan issue would be similar. If the general thought among breeders was that "true" roan (ie, QH roan that was tested) was embryonic lethal, wouldn't serious breeders shy away from breeding two roans because they make their money producing foals? I don't think many stallion owners would even breed their roan studs to roan mares if they felt there was a 25% chance of no live foal on top of all the other hazards involved in getting a live foal.

Backyard breeders might do it because they don't know better, and there might be some "catch foals" born from roan-to-roan, but I think the popular belief would so limit the numbers of roan-to-roan matings that there would only be a small population of horses produced from roan-on-roan.

[Pan Zareta]

UC Davis' page describing their roan zygosity test makes it clear that they have not identified the mutation that causes true roan, and are testing for markers near it. Obviously, the late Ann Bowling's work there proved that true roan is not an obligate homozygous lethal. But it doesn't necessarily follow that true roan is never homozygous lethal. The records and observations of some breeders suggest it can be. Assuming that these breeders have correctly distinguished between true roan and roaning, there are several plausible scenarios that could explain their findings. As XFF suggests true roan may have multiple alleles, some of which are lethal in combination. Another possibility is that it is homozygous lethal only in the presence of certain alleles at other genes.

[xfactor fan]

I'd like to make a distinction between early embryonic lethal, and fetal lethal.

With the embryonic lethal the mare comes into heat, is covered, conceives then the embryo fails to implant. She then comes into season again and is covered again and may take this time. Most times the humans may not even know that there was a embryonic lethal involved. And if the mare double ovulates, one egg may have the lethal, while the other might not, in this case no one would ever know that there had been a problem.

Fetal death is slightly different, where the mare carries the foal for a significant amount of time, up to delivering a foal is either stillborn, or dies in a few days after birth. This situation is much harder on all parties, the mare, and the humans. It also results in the loss of a reproductive year for the mare.

As Pan Zareta pointed out there could be other things going on, but the simplest explanation of the skewed ratio of Roan x Roan births in some roans, and the barren mares and late births is that there is some mechanism at work that eliminates embryos that are RnRn.

I'll try to find the paper on the two versions of Roan, the creaky memory is saying that it was written by the other Doctor Bowling.

[Jorge]

I'll try to find the paper on the two versions of Roan, the creaky memory is saying that it was written by the other Doctor Bowling.

Would like to have a copy of Dr. Bowling last article on roans.

[Pan Zareta]

I'll try to find the paper on the two versions of Roan, the creaky memory is saying that it was written by the other Doctor Bowling.

Dr. Ann Bowling died 10 yrs ago this month. Per the article in 'Quarter Horse News' (15 Dec 2004) her husband, equine geneticist Michael Bowling, 'put the final touches' on her manuscript for the roan study and genetics staff at UC Davis were preparing it for publication. But I can't find any record that it ever actually appeared in print.

Would like to have a copy of Dr. Bowling last article on roans.

I hope XFF can locate it. Until then, here's a link to the synopsis in QHN
http://www.hancockhorses.com/article-roanQHNews.pdf

[Jorge]

Thank you very much for your fine solicitude in trying to assist me on this one. Yes, I know about this very interesting synopsis
( http://www.hancockhorses.com/article-roanQHNews.pdf ).
Thanks again!

[Linda_d]

Before the AQHA accepted cremellos and other double dilutes, and when many breeders thought palomino-to-palomino matings produced "albinos" (actually cremellos), very few AQHA breeders would intentionally breed palominos to palominos because they didn't want unregisterable foals.

I think the roan issue would be similar. If the general thought among breeders was that "true" roan (ie, QH roan that was tested) was embryonic lethal, wouldn't serious breeders shy away from breeding two roans because they make their money producing foals? I don't think many stallion owners would even breed their roan studs to roan mares if they felt there was a 25% chance of no live foal on top of all the other hazards involved in getting a live foal.

Backyard breeders might do it because they don't know better, and there might be some "catch foals" born from roan-to-roan, but I think the popular belief would so limit the numbers of roan-to-roan matings that there would only be a small population of horses produced from roan-on-roan.

I think I stuck my foot in my mouth. After reading xfactor's link to the Hancock Horses page, there seems to be a lot more people who breed roan to roan than I would ever have thought, given that the original article on dates from 1977.

[xfactor fan]

The old synapsis are saying that the article was written by Michael Bowling. And was sort of a unified field theory on roans.

The breeders were all up in arms about what they were seeing--the lack of the RnRn horses reflected in the 1:3 ratio of roans to non-roans. While there were those pesky roan stallions that were siring 100% roan. And then there were the critics of A. Bowling's unpublished study, with folks up in arms about methodology. Lots of talk about her calling non-roans, roans. All in all lots of upset folks on both sides of the debate.

This particular soap opera has been unfolding for the last decade, and honestly I'd been coming down on the bad methodology side of the argument. Then the info about the Hancock roans surfaced, which of course complicated matters.

The idea that there were two different roan mutations made a whole lot of sense--and explained what the breeders were seeing, and what the scientists were seeing.

And if roan is indeed a KIT mutation, looking at the work done on both Sabino--lots of versions--DW--lots of versions, the idea of several versions of roan doesn't seem all that strange.

[Pan Zareta]

I'd been coming down on the bad methodology side of the argument.

Based upon remarks p. 40-42 in her book Horse Genetics (1996, CAB Int'l.) I think Ann Bowling knew how to distinguish true roan in phenotype. The aspect of the study that I find questionable is her reliance on the AQHA stud books to determine coat color of horses that couldn't be observed directly. Some names shown as "roan" therein were not true roan. Ditto entries in some of the TB registries. To date, the roan gene has not been documented in the TB, but there are plenty of "roans" in the stud books. I haven't made a study of it, but I'd bet that most of them that weren't actually grey were rabicanos. The TB mare in my avatar is a rabicano, but out here in cowboy country most folks call her a roan - in spite of my attempts at enlightenment.

[xfactor fan]

I'd been thinking along the lines of confusing regular roan with minimal appy roan. (LP) Old time QH folks don't much like the notion that there is "spotted blood" in their horses. And now with the change of the white rules there are "crop out" QH's with full blankets showing up from mostly solid parents.

And to be fair to the QH folks, minimal LP can look like a solid horse, or a regular roan. And it can take a while to develop, so the horse may look solid at the inspection, but color up later.

No disrespect intended toward Dr Anne Bowling, but she passed away before the study could be published, and there's no way of telling how she might have refined her data before publication.