A Note about Sugarbush Draft Horses
I see it over and over again, and no matter how many times it's said, it's still wrong. "Sugarbush Drafts are just an Appaloosa Draft Cross". Uh.... no. The Sugarbush Draft Horse was a breed created many years ago in Ohio. While the initial cross was made using Percherons to Appaloosas, in the many generations following, the breed has been solidified into a consistent type. Saying these horses are "just" a draft cross makes as much sense as saying that AQHA horses are "just" a Thoroughbred cross, American Cream Drafts are "just" a dilute Belgian, or that Morgans are "just" a grade.
Wednesday, July 21, 2010
The basics of white patterns
My father used to always ask me jokingly, "Are Zebras white with black stripes, or black with white stripes". Once I got into genetics, I was able to answer that question. Zebras are black with white stripes like this picture shows.
The reason is that white markings are actually areas where the pigment production is inhibited. This means that those cells still have the code for the horse's (or equid's) base color, but something prevents the color from being produced. That "something" could be many different things, from specific genes to outside factors. If you keep in mind that a foal starts as a single cell, and as it develops that cell divides, and then those cells divide, you can see how early cells will end up far from other early cells, but later cells will be close to each other. When the embryo is only 2 cells, one might end up at the tip of the nose, while the other will be the tip of the tail, but in a near term foal a new tail cell will be next to a new tail cell.
Genetic decisions (which genes are activated) are altered through out embryonic development. Cells are "triggered" to be skin cells, or heat cells, hair cells or hoof cells, depending upon many super technical bio-mechanical things. Never fear, I won't dork out on those, but it does help to have a basic grasp of this phenominon to see why patterns vary so widely! Specific triggers can cause genes to be activated, and changes in the body to occur. An example of this is how a newborn takes it's first breath, but before that the baby gets oxygen through the umbilicus.
First of course, the DNA coding is the "blue print" of what will happen, but just like in construction, things don't always go as planned. Things such as temperature, position (is the foal pressed against the uterine wall) gestational time, nutriton, and a myriad of other factors all have their role. A good analogy for this is such construction problems as: expansion of materials in heat, misreading the blue print (yes, this happens in DNA too), and poor building supplies.
Here is an example of some face markings from clones of Smart Little Lena. These horses have exactly the same DNA, but the difference in markings is due to "external" factors like I mentioned above. No, we don't always know what did what, but examples like this allow us to take steps to figure it out.
There isn't a more perfect example of the difference between nature and nurture then clones. Nature includes DNA, while nurture includes just about everything else. Each of these foals had a different surrogate dam. Differences in the mare's average body temperature, location of the foal in utero (right horn, left horn, lots of room or cramped in there) all can change things even though the DNA is the same in each one.
Head hurt yet? Yeah, it gets worse.
Now, pattern genes basically code for pigment to NOT be produced. Because of the way the foal's cells develop while it's a fetus, this results in pigment cells being next to similar pigment cells. Think of a paint horse. Big blobs of color and white are caused because of this. Also, the path of cellular development can cause patterns to appear. You can often see the cellular pattern in leopard appaloosa colored horses like this guy:
All horse markins will be affected by that. This is why you don't see sideways blazes, or appaloosas with only a spotted area on their heads. It's all about what cells are first and which are last. In explaining patterns over the next few days, I will refer to this migration of cells, and how some things depend upon external factors to get more "bang for the buck". Appaloosa is one of them.
Also, just a bit of trivia for you: This pattern of migration is also why sooty tends to be top down, pangare tends to look like it comes from the bottom um, and why agouti pushes the pigment to the points. For me, learning about cellular migration was one of those things that made everything else fall into place.
Again, if I've lost you some where and you feel like your head is about to explode, please feel free to email me. I will explain things in different ways, I'll try over and over. I know many people are very interested in horse colors, but genetics don't come easy to them. If you want to know, but don't want to feel selfconscious, simple send an email to me at: firstname.lastname@example.org
Today, I only have an opinion question. While digging up the clone pictures, I saw many discussions based around breeding to a clone. Some people commented that because a clone might not have the same performance ability, they wouldn't think about it. Others would if only their registry would allow it. So, would you, or would you not ever breed to a clone (assuming you were wanting to breed a horse)? Why?