Uncategorized


Holiday2012

Seasons greetings to all our readers! Thank you so much for joining us this past year. Your ideas, questions and photos have enriched the discussion, and I am looking forward to another colorful year.

This post ran back in the spring, but I never did add the promised page of links. That is up on the website now, though it is still a work in progress. Clicking on the “Genetic Diversity” tab up at the top of this page will take you to a link. 

The Equine Tapestry

My oldest son has been struggling with freshman Biology, so the concept of evolution has been on my mind a lot lately. I have also been reminded that evolution applies, not just to organisms, but of points of view. Sometimes it can be easy to forget that you once held a different view – unless of course you are foolish enough to write it down for others to find later. I have been writing about horse color long enough now that I have had that happen!

The reminder of this came from my husband. Longtime readers of the blog have probably picked up on the fact that I have a strong interest in the issues surrounding genetic diversity. It is, as I have mentioned, one of the themes that runs through the upcoming books. My close friends could probably warn readers that it is a tempting soapbox for…

View original post 1,734 more words

My previous post about white on the faces of tobianos, made before I left for a trip to Boise, generated a lot of discussion both here and on the Equine Tapestry Facebook page. I thought it might be helpful to expand a little on the subject.

Before researchers had the ability to examine color mutations at the molecular level, what we had was analysis of phenotype (how the individual horse looked) and production records. In older articles on color genetics, those were the tools that were used. Analysis of phenotype is still very popular among people who discuss color on the internet, but the appearance of an individual horse – or even just that horse and his parents – only tells part of the story. Extended production records are needed to get a more complete picture. These can show patterns of inheritance across a broad portion of the population, and that can give clues about the nature of the colors and patterns involved.

Looking at these broad trends requires a lot of data, and one of the biggest limitations is that the kind of information needed is not always retained, or if it is, it is not always easy to access. When I wrote an article in 1997 speculating that some horses being identified as dominant white might actually be “maximum” sabinos, it was because I had noticed trends in the early Walking Horse stud books. Unlike many other books from that time, the entries there listed markings (and eye and point color) in detail. Perhaps even more important, at the time was doing the research behind the article, I lived a short distance from the registry where I was given access to records and archived materials. With extensive family records for hundreds of white-born Walking Horses, I was a lot more confident that what I was seeing was a form of sabino.

On one of my visits to the registry, I ran into a breeder doing research on what would eventually be known as the champagne dilution. In the course of explaining what I was there to find, I mentioned that the phenomenon of white foals did not seem to occur in Clydesdales, even though they were uniformly sabino and many of the patterns looked quite similar to those on Walking Horses. The breeder asked if I had Clydesdales, too. When I explained that I just had an aged Walking Horse and a small pony of unknown origins, she expressed confusion about why I had a set of Clydesdale stud books. The reason was that in the pre-internet era, stud books were one of the few ways to obtain information on whole families of horses. Each breed, and therefor each set of stud books, offered a different “control group” to study different patterns. If Clydesdales, for instance, could be assumed to have sabino but not to have frame, then all the patterns in the breed represented what was possible with sabino alone.* In Paints, where frame was common, the possibility that frame was influencing the pattern was always there so until tests were developed it could not be ruled out as causing white on any given horse.

These control groups were not perfect, since the records could contain errors or omissions, but it did make it possible to identify trends. It might not be possible to prove something, but it could suggest useful avenues for testing ideas.

So what does this have to do with white on the faces of tobianos? Well, the suspicion that some tobianos had face white unrelated to sabino, splash or frame came because it was happening in breeds that were my most reliable control groups for “pure tobiano” because the solid members rarely had white markings of any kind. These were Old World breeds with long-closed stud books, so frame was not likely to be present. Sabino (as we currently understand it) did not appear to be present, and my hope for proof that splash was involved was coming up empty. Why then did so many tobianos have white faces? Why were quite a few quite oddly marked on the face, or blue-eyed? Was it not a coincidence that so many homozygous tobianos – in all breeds – had white faces?

Unfortunately for those of us who live in the United States, it is harder to gather information directly because most of our breeds have markings of some kind, and sabinos of all types are extremely common. The horses in this post, and the horse in the previous post, are all American Paint Horses. Finding a Paint Horse that looks “pure for tobiano” is difficult, and even then it is quite possible that he carries the gene (or genes) for ordinary markings. Those are currently believed to be caused by a recessive mutation to the KIT gene.

That means that this guy, who appears to have only tobiano and no significant white on the face, might carry that mutation and produce offspring that have white on the face.

What was intriguing was not just that white faces seemed to appear on these tobiano ponies, but that an increase in white on the face of the tobianos did not seem to translate into an increase of white on the non-tobianos. That is what might be expected if the tobianos had a separate mutation creating white markings, either the previously proposed KIT mutation or something new. Were they separate but linked? Or was it simply a part of the pattern itself? Was it both, and if so which forms were caused by each?

Or was I misreading the situation based on limited data? What role was selection, both by breeders and by owners, playing in this?

That is why I found the situation with the Polish Hucul so interesting. Because there are conflicting interests, and because patterns can often create strong opinions on the part of breeders, it is hard to know how to weigh claims that the presence of markings on the tobianos threatens the unmarked nature of the solid population. But the question about whether white on the face might be intrinsic to the pattern is a valid one, as is the question about whether or not an existing KIT mutation (like tobiano) predisposes the resulting foals to new (de novo) KIT mutations that add further white. These questions also tie into the larger questions about the nature of white markings and their relationship to the different white patterns.

* Sabino is now understood as a category of patterns, rather than the one pattern it was believed to be then.

Just a quick note that the previous post on dogs was composed during our family’s annual trip to Pawleys Island. I am still shaking the sand off my feet and realizing just how much was left undone while I enjoyed the live oaks and the azaleas. If you are waiting for a reply from me, or if your message was caught in my (over-vigilant) spam filter, don’t give up yet! I should be caught up in the next day or so. (Or at least as caught up as I ever actually manage to be!)

I am a big believer in the benefit of grouping images of horses of a specific color or pattern as a way to develop a solid mental image of the different colors. For those of us that paint horses, it is the single best way to develop your eye. Back before there were many horse sites on the internet, I kept clipping files. The down side was that my ability to collect images outpaced my ability to clip them from magazines and sort them into scrapbooks. I still have boxes of unsorted images from that time! With the computer, it was much easier to sort images into folders and I assembled hundreds of thousands of references.

What I have not been able to do is share them. As anyone who has followed this blog for a while knows, I am a stickler for intellectual property rights. I stick with pictures that I have taken, that are in the public domain, or that I have been given specific permission to use. I would love to share my sorted images, but I do not own most of them. Keeping a library of images for personal reference is quite different from posting those same images on a public website. Which brings me to Pinterest.

Pinterest has been described as a virtual corkboard, but really it is a social media site for the sharing of links. The site allows users to assemble groupings of links by topic, and then uses a thumbnail as a visual for that link. Most people use it to share images of products and ideas that they like. For me, I saw it as a great way to put together some color sorting files that linked directly to the source (ie., the owner or farm that had the horse), while still giving an overview of the range in a particular color or pattern. The image above comes from a board I started with images of homozygous tobianos. What I was specifically interested in was the range of face markings, because I had noted that even in breeds not inclined to face markings, the homozygous horses often had a fairly high level of white on the face. Looking at a lot of them, from a lot of breeds, might be helpful to see any trends. I also have a board for tested SW1 splashes, tested Sb1 sabinos, and the Bald Eagle line that has tested negative for splash. Eventually I hope to add more boards for other colors and characteristics, because I think this might be a particularly good way to share visual information.

For those that are not currently using Pinterest, here is a good overview of how the site works. You’ll notice that you do have to request an invite, since the service is actually still in Beta mode. This can take a few days, in my experience.

(Oh, and I must apologize that I have not found a way to separate out my personal Pinterest boards from the horse color ones. So beware that there are boards for recipes and craft ideas and pretty artwork all completely unrelated to the topic at hand!)

I want to thank everyone who has shared their testing results this last week. Results have been coming in, and new horses are being sent for testing. Meanwhile, I have been slowly updating the lists on the Splash Project Page as I get the information. You’ll see a lot of horses have been added, including homozygous, heterozygous and negative tests. The only thing we are missing at this point is any horses that have tested for SW2 or SW3, so those remain a mystery for the moment.

There are still more results to add, and still more horses with pending tests. As some of you are aware, I was called home to Alabama for a family emergency. That means my ability to post pictures will be somewhat limited until I return home. When I get back, I will add those and get back to some of the unfinished blog posts on non-splash topics.  (If you have a horse on that Splash Project Page without a photograph, but want one included, just send me a message. I do not post photos on this blog without specific permission, but I never turn down someone who will allow me to use a picture!)

The blog has gotten a big influx of subscribers in the last week, so I wanted to send out a welcome to everyone who has joined the conversation. Because that is how I see this blog – as a conversation – please feel free to comment on the posts. I have been battling a nasty head-cold these last few weeks, so I am a little behind both on private replies and posts, but I am always interested in hearing what others have to say. Many times it is questions that are sent that serve as a jumping-point for later posts.

The upcoming week should be an exciting one, since the first of the Splash White test results should start coming in. I will be updating the Splash White Project page over the weekend, since there are more pending horses to post, and will post the results as they are known. I also have an assortment of dog color posts lined up as well, because that is a tangent I often explore here, and another group of posts on appaloosas. Hopefully I won’t whiplash everyone too badly if the topics switch around a lot!

Next Page »