we now know that the LP gene is the first gene in appaloosa coloring, but what makes the difference between all those crazy appaloosa pattern? It's the pattern genes. There's a whole whack of them too (yeah, that's a technical term... whole whack). So, lets see if I can phrase this in a way that doesn't make anyone's head hurt too bad.
The LP gene, or Leopard comPlex gene, is like a switch. On its own, it doesn't do a whole lot. Over time a horse with only a dominant copy of LP, and no pattern will get an appaloosa color appearance, but it could be minimal, and right now there's really no way to predict it. But to get a horse with an obvious pattern at birth, you need to have a pattern gene... or a few.
The pattern genes aren't just for pattern. A few examples of minor pattern genes include base color (black, bay, chestnut bases) or things like sabino, splash, and other pinto genes. If you remember how we talked about the pinto genes and their minimal forms that show only as face and leg markings, you can see how often these genes are included in appaloosa colored horses, as well as Appaloosas (as in ApHC registered horses).
The first thing to understand about pattern genes, is that we use the symbol PATN for a domiant copy, and patn for a recessive, but this is really incorrect. Because there are MANY pattern genes, we should not refer to them as if they are the same. Because we don't know where they are, and what genes specifically they are, this type of language makes it much easier to converse and be understood. Basically, it's genetics slang.
We call this gene PATN1. Horses who do not have the leopard pattern gene are patn1patn1. Most horses that DO have the leopard pattern gene are PATN1patn1, because there are just very few breeding programs that breed leopard lines to leopard lines. Right now, leopard is the only gene I know of that has been assigned its own number. The rest of the genes are just refered to as patn or PATN.
Now, just to make it even more confusing, appaloosa patterns are not controlled only by LP and PATN. There's also the "enhancing" and "supressing" genes. These enhancing and supressing genes affect the way that the pattern is displayed. From big spots to small spots, from lacy edges to crisp edges, from a lot of white between the dots to dots crammed almost on top of each other... this is all done by the enhancing and supressing genes.
Some of these enhancing and supressing genes have a small pattern effect on their own. As you can see, a lot of genes get to do "double duty" in horse color. And I can't stress this enough, there are around 30 different genes that could make some form of white pattern at birth on an appaloosa colored horse. Each one of those genes has a dominant and a recessive allele, and a horse can have any of the 3 combinations (homozygous dominant, heterozygous, or homozygous recessive) at that particular gene.
While a horse with at least one copy of dominant LP will always show its largest pattern, a solid horse doesn't show its pattern. This makes it pretty much impossible to know what pattern genes a solid horse carries. You can make educated guesses based upon the ancestors of that horse, chances of inheritance and number of progeny, and a whole lot of mind numbing math. But seriously, who wants to do THAT? (I love genetics, and the math really makes MY head hurt!) So, when predicting the exact color pattern of offspring, it gets REALLY confusing!
Lets use my homozygous stallion "The Polecat" (aka Spot) as an example. Yes, I know he has an unfortunate name. What I wouldn't give to change it!
As for patterns though, he has just about every pattern out there. He does not have PATN1 though. While he's almost all white, much of that is due to roaning with age. Ol' Spot is 13 this year, and that means he's had 13 years to gain more white. When he was younger, he looked like this:
A horse will show the largest pattern that they have, and you can only guess at the smaller patterns because of their parents or offspring. Because Spot has had a LOT of offspring (24 before I purchased him) I have a really good idea of what he can throw.
From minimum to the largest:
Scorch - E? aa, LPlp patnpatn. Yes, he really does have appaloosa characteristics, although very very few.
If you notice the progression of base color above: Black, then bay, then chestnut. This is the exact order of supression/enhancement that the horse's base color gives to the pattern. In otherwords, it's likely that these 3 horses actually have the same pattern genetics, but more white is able to show with the "easier" colors. Black is the hardest.
In Spots life, he's only every had 2 foals born with no white at birth. Scorch, and a black filly. I find that very interesting, as the odds say it's not likely to be such a small number. Therefore, it's my belief that Scorch really DOES have a small pattern, but has every possible gene to suppress that pattern. (This is just my theory, based on the numbers). If that's true, then it would mean that Spot is homozygous for this small lacy blanket pattern.
From there, we get bigger:
Sorry, I don't have a chestnut version of this size pattern.
Again, I don't have a chestnut (I only had 2 chestnut foals from Spot... what can I say, I have a ton of black based mares, my chances of chestnut are low).
Now, the interesting thing, is that the base color alleles seem to be additive in their enhancing or suppression. So, a horse that is EE would have a more supressed pattern then a horse that is Ee, and that would be more supressed then a horse that is ee.
Agouti seems to be an enhancing gene. Again, a double dose enhances more then a single dose. None of these horses can be double agouti though, simply because their sire is black (homozygous recessive for agouti).
Then there's the face and leg markings. If you notice, I tend to have 3 classes of face and leg white markings. The first has only minor face white (small blazes, or stars) with no leg white. The second group has moderate face and leg white (larger stars/blazes, with one or 2 socks) and the last is high white (big blazes, 4 white legs). The first group I am not positive of what they have for genetics there. Maybe sabino? Maybe it's a natural birthmark type of thing?
The second group has sabino in a very minimal form. Spot has this, as do many of my mares. You can see that Scorch and Diva both have this type of markings. The last group are splash whites. Most of those also have sabino (from Spot, their sire). What can I say, I really like mares with splash white!
But, Sabino and splash are pattern enhancing genes. Sabino tends to make the pattern all lacy around the edges, and make the polka dots really small. Sabino is basically invading the colored area. Often when people hear "enhancement" they thing "better". In this case it just means more white.
Splash on the other hands enhances in a different way. It makes the white stretch out. Think of this like a picture drawn on a balloon. As the balloon expands, the lines get further apart. While sabino results in the tiny dots that so few people desire, splash simply puts the pattern on steroids. Unfortunately, sabino is so mixed into most horse breeds, that it's almost impossible to get it out of the appaloosa pattern genetics.
I often have people ask me how to get those big monstrous polka dots. That seems to be the most desired pattern. Who cares how big of a blanket they have, so long as the dots are HUGE. Well, this goes back to the sabino. Horses with big polka dots seem to have no, or very "little" sabino (there's thought to be 8 types of sabino.... they aren't clearly defined yet, so when I say little, I mean one of the less enhancing versions). If you breed appaloosas with little to no face or leg white, and large patterns, then you will likely end up with large polka dots. It's really that easy.
And to show you an example of a leopard with large spots... here's Siri. This is Q's latest foal, bred by Sigrid Ricco. Siri is owned by Kris Hartman, in New York.
Next, I will be putting all of this together. Unfortunately, there's just too much for a single blog post!
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.