Filling in

Not the best photo, between the shadows and the shave lines, but he's been an adventure to photograph.

Another cold weekend, complicated by various things (including a late night, a spousal stomach bug, and assorted other fun), meant I didn't get out to the barn.  Instead, have the above picture of a 10 month old Justice, in what is probably the one full-body photo I have of him from 2016 that isn't thoroughly embarrassing.  (Poor baby boy.  I keep thinking of the rule of thumb from the Chronicle of the Horse breeding subforum: three days, three months, and three years are the ages where you can best see what you've got.  Three days and three months?  Beautiful.  C'mon, three years...)

Instead, I figured I should probably explain what the heck I'm talking about when I talk about Justice's color and genetics.

I'm not going to go into color genetics right now, other than to note that I can make some basic assumptions about Justice's.  His father is a chestnut; his mother is a bay.  So I know his extension gene (the thing that determines if you start from a black or red base) and I know part of his agouti gene (the on/off switch for bay, only visible if your base is black).  He has to be Ee A?, because he's visibly bay!  I also feel pretty confident that he doesn't carry cream, dun, or grey; with all three, if you have one copy of the gene turned on, you're going to show it, no matter what base color you've got.  Neither parent is grey, neither has dun, and dad definitely isn't carrying cream, because he's chestnut and not palomino; while it's possible that mom could be a buckskin, she presents as a pretty classic dark bay.

I'm also not going to talk too much about the non-Appaloosa white patterns.  There are a metric butt-ton of them (from the classic paint tobiano, frame overo, and splash to the roans, rabicanos, and sabinos to the dominant white/white spotting, which depending on which one a horse has, what they look like).  If there's interest, let me know; I don't have a problem talking about them - the Ws are particularly fascinating to me - but for talking about Justice, none of it matters.  His registry says no tobiano, no frame, no dominant white, and no to certain types of splash; dad's been tested and carries none of it, and while it's possible that mom might carry one of the ones that likes to hide (frame, for instance), she wasn't required to test.  So we can assume he has none of them.

These two are great examples of classic tobiano.

Classic frame, with the addition of a bald face and some leg markings.

Pretty sure this guy is either splash+sabino or splash+dominant white.

Instead, I'm going to talk about the two parts of the Appaloosa genetic shenanigans.  Part one is what's referred to as the Leopard Complex gene (or LP).  Part two is the PATN genes, the ones that actually dictate the pattern.

LP is an off-on-REALLY ON switch.  If both copies are off, you've got a solid horse.  It doesn't matter what PATN genes the horse might have; they're never going to show, because the thing that activates them is LP.

Hmm, this example looks familiar...  Cessa is known to carry at least one PATN gene, but has no LP - so nothing shows.

If one copy of the LP gene is turned on, then the PATN genes can start to show.  That's when you can get patterns with lots of spots, big or small.  That's when the mottled skin, white sclera around the eye, and striped hooves show up.

Cessa's 2015 foal, Reign of Stars - one copy of LP, and at least one PATN gene. Also Justice's half-sister!

If both copies of the LP gene are turned on, then three things happen.  The PATN gene will show, of course - but the spots vanish or almost vanish, leaving vast white territory.  And the horse will be night-blind.  Horses with both copies of the LP gene turned on produce what's commonly referred to as fewspots - the fully white Apps and the ones with white blankets with no spots on them.

One of the horses at the barn - LP/LP with a heck of a blanket.

The PATN genes are where most of the research into Appaloosa genetics is concentrated right now.  They know that no PATN genes means a horse that can only display Appaloosa roaning (aka varnish roan).  Varnish roan can look very similar to classic roan, but it has one very specific characteristic aside from the Appaloosa stuff (striped hooves, etc): they tend to retain dark areas over prominent bones.

Like Justice's daddy here

And the roaning isn't just limited to horses with no PATN, although it's only called varnish roan when there aren't any other patterns.  Any horse with LP can roan in the non-patterned areas of the coat.

Some horses roan quickly; some don't.  I know one LP/lp individual who is creeping up on 10 and has a few roan patches - and that's it.  On the other hand, Reign looks like she means to shed out almost pure white this spring - and she's only a couple of months older than Justice.

Research has also shown that PATN1 controls large areas of white patterning that cover 60-100% of the body.  Most leopards will have PATN1.  PATN1 is the first (and at this time the only) pattern gene available for public testing.

All the other patterns seem to be built via multiple different PATN genes, very few of which have been identified. For example, they know that PATN2 is related to the blanket pattern, but it's not a strict 1 to 1 relationship; the size and shape seem to be determined by other PATN genes, so a horse with a spectacular, large blanket may or may not pass it down.

Most of the research about LP and the PATN genes is coming out of The Appaloosa Project, and they're still working to understand it.  Any mangling here is totally my fault.  :)

Now, all that explained... when I natter on about this little face:

And what he's got going on with his LP, I've got some thought processes going on:

1. I know dad was tested as LP/lp.  I know mom is the daughter of a Percheron and an Appaloosa, and I know she shows the characteristics of having LP, so she can only be LP/lp.
2. I know mom doesn't have any PATN; aside from her random traveling spot, she doesn't have any white at all.
3. My best guess at dad's pattern is that he's got a blanket.  He's pretty thoroughly roaned out, but he's got spots in roughly the right area for a blanket and two of his three foals bred at the farm have blankets.
4. I know Justice has at least one copy of LP, from one of his parents, because he's got those Appaloosa characteristics.  Based on #1, that means he can only be LP/lp (2 in 3 chance) or LP/LP (1 in 3 chance).
5. If you've got LP and a PATN gene, chances are you're going to see it before the foal is weaned, if not at birth.  Every LP baby I've ever seen, if they had a pattern, it was there at birth or shortly thereafter.  Justice came out brown, continued to be brown through weaning, and honestly didn't show anything but brown until last spring.  So I'm willing to bet he's a varnish roan.

Since I don't plan to breed him (brain surgery this spring!), my wanting to know if he's got one LP or two is about half curiosity; the color of future generations does not depend on this.  It's fascinating that he's throwing out roan spots while his mother stays pretty much solid, because it implies that he's got something she doesn't - and it sure doesn't seem to be a PATN gene.

On the other hand, it is actually kind of important to know if he's night-blind.  Two copies of LP turned on and night-blindness are inextricably linked.  You can't separate them.  You got one, you got the other.  Not that I'm likely to go night riding any time soon, but it will affect how I approach taking him in and out of barns and trailers, and it will affect boarding if I should need to move him from where he is now.