Pinto Pattern Expression

[Scribbler]

I think I understand the probabilities of a foal inheriting a frame overo or tobiano gene: 50 % if the parents are both heterozygous, or one heterozgous + one no pinto gene, and 100 % if one of the parents is homozygous (obviously, that only applies to tobianos, as a homozygous frame overo dies at birth).

(OK, as JB points out my math is wrong here. With heterozygous parents, the foal has a 50 % chance of being heterozygous for the pattern, a 25 % chance of not getting the gene at all, and a 25 % chance of being homozygous for the pattern, which is fine in tobianos, but lethal white in overos)

But is there any research on what governs the expression of the pinto genes that a foal inherits? Pinto (both frame overo and tobiano) can express itself as anything from mostly white to mostly dark. I did a search on this topic on COTH and it looks like, in the older posts, the most informed commenters were saying it was quite random. Is there any new information on this?

I haven’t been able to find anything clear on this on the horse genetics, pinto or Paint websites.

I realize patterns get more complicated when you mix different pinto patterns into tovero, or add splash and sabino to the mix.

I’m not planning on breeding anything, but co-incidently I had a tobiano pony mare as a kid, and find myself with a frame overo Paint mare as an adult, so I’ve been interested in the patterns my whole life. The genetic knowledge didn’t exist when I was a kid, so it’s interesting to see where it confirms, and where it changes, what people thought they knew back then.

[JB]

If both parents are hetero for 1 pattern, then it’s a 75% chance the foal will get that 1 pattern, 25% chance of getting it from both (which is why you NEVER breed 2 Frames together :no:) and 25% chance of not getting it at all.

If one is hetero and one doesn’t carry, it’s 50/50

Expression is a very different story. At least with Tobiano, it’s nearly guaranteed it will be obvious. How much white though depends. Some horses, like Sempatico (who is not a minimal Tobi) are really good at producing more minimally expressed Tobis. He’s got loud ones too, quite a lot, but he also has so many more minimally expressed ones. Most don’t do that though.

Frame is much more random. Very loud parents can produce solid carriers, and vice versa, and anywhere in between. Very loud is not terribly common. But, with the Overo patterns (all of them, not just frame, as well as the appy patterns too) there are other factors Black-based colors will be less loud than red-based colors, all else equal. The more black pigment, the more white suppression, so blacks are the most suppressed, then the dark brown, then the lighter browns and bays, then the reds are the most expressed.

Certain patterns have been shown to multiply effects. Frame and one of the DWs tend to make for very loud patterns, for example.

[Scribbler]

[QUOTE=JB;8240868]
If both parents are hetero for 1 pattern, then it’s a 75% chance the foal will get that 1 pattern, 25% chance of getting it from both (which is why you NEVER breed 2 Frames together :no:) and 25% chance of not getting it at all. [/QUOTE]

Yes, my math was off here! I figured that out later at night after posted this, when I was mulling this over but not near the computer

Do homozygous tobianos have “better” markings than heterozygous ones? I understand they can have little “paw print” markings. The homozygous tobiano Paint studs I have seen on line tend to have “good,” balanced markings, if the ideal is still 50/50 white/colour. But they may also have been chosen for those markings as well.

[JB]

Nope, there are minimal ToTos and loud Totos. The paw prints/cat tracks are often considered a sign of ToTo, and while that’s usually the case, it’s not a guarantee.

You’re right about the 50/50 being considered ideal (as well as placement of the white), at least in the APHA world and for the Tobis (they want LOTS of white on their Frames). And yes, to some degree, that can be selected for in the Tobis.

[littleum]

[QUOTE=Scribbler;8241162]
Do homozygous tobianos have “better” markings than heterozygous ones? [/QUOTE]

No, this mare is a cryptic tobiano and is T/T:

https://scontent-lax1-1.xx.fbcdn.net/hphotos-xtp1/v/t1.0-9/10389987_834539679908729_8713420943866020199_n.jpg?oh=fe47ae7487b870001a3d655ecc31d1c0&oe=565BBFB9

https://www.facebook.com/128662503829787/photos/a.171563002873070.41222.128662503829787/879641028731927/?type=1

[Nootka]

what is cryptic tobiano?

( I can’t view any of these links from work)

[JB]

Minis break rules

I think she means “minimal” tobi. Minis are notorious for being extremely minimal

The in the links has 2 low socks - fetlock-high - and what looks like maybe a dot on the inside of another leg. That’s it. Yet s/he is homozygous Tobi.

Not uncommon in minis, extremely rare in regular horses.

[littleum]

[QUOTE=Nootka;8241295]
what is cryptic tobiano?

( I can’t view any of these links from work)[/QUOTE]

It’s a tobiano that does not actually look tobiano, and you don’t know their tobis until they throw a tobi foal or the DNA test comes back.

It’s extremely rare in Miniatures too, and I’ve only ever seen 1 big horse that was a cryptic.

But overall, yes, chrome is pretty uncommon with miniatures. You just don’t see a lot of socks or white faces without accompanying body white. If there’s face white it’s usually a snip or a star, maybe a small blaze. Used to drive my vet CRAZY when doing coggins diagrams. XD

We have a lot of minimal pintos. Stuff like LWOs who only have the wide blaze and a blue eye, or tobis who have a patch of white on their withers and then high socks behind, maybe a little white around the tail. Lots of those.

[JB]

I don’t know that it’s “extremely rare” in Minis, as I am not in the mini world and have seen quite a few. Maybe that’s only because I go looking for them, but they aren’t hard to find

I would actually suspect Tobi in that mini because 1) it’s a mini and 2) the white just looks…wrong for an Overo/KMOSS presentation. I would say that Tobi in this really minimalistic form is pretty rare. Most of the “cryptic” (never heard that term!) forms have a bit more tell-tale sign to the educated eye, though still don’t even whisper “Tobi” to the uneducated. Most of those have a high leg that’s easy to classify as Splash, but it’s wrong for even Splash.

Hidden frame is present everywhere - minis, ponies, horses. Totally solid, or a bit of face white. Quite a few horses also have the wither and dock of tail white with some (often not all) tall white socks as their only Tobi white, that’s the most common minimal form in horses. I’ve seen 2 regular horses who present much like this particular mini - just low socks.

[Scribbler]

OK, so it seems like colour expression in pintos is quite random, whether the parents or foal are heterozygous or homozygous (this last doesn’t apply to Overo, obviously).

Do individual mares or stallions tend to reliably produce foals with “better” markings than other mares or stallions? I suppose no single mare has enough foals in her lifetime to give statistically meaningful data. But there must be stallions out there with 100+ offspring. People do advertise pinto/Paint stallions as “guaranteed to throw colour.” But even then the range of patterns they show for foals is quite varied.

[Simkie]

[QUOTE=JB;8241417]
Minis break rules

I think she means “minimal” tobi. Minis are notorious for being extremely minimal

The in the links has 2 low socks - fetlock-high - and what looks like maybe a dot on the inside of another leg. That’s it. Yet s/he is homozygous Tobi.

Not uncommon in minis, extremely rare in regular horses.[/QUOTE]

Jorene Downs had one years ago–foal by a homozygous tobiano came out without a STITCH of white on it, IIRC. DNA test came back as it should. I wonder if the info is still on her site?

Nope, but wayback still has it. (She does have a star and a little sock!)

[JB]

@Scribbler;8244155

OK, so it seems like colour expression in pintos is quite random, whether the parents or foal are heterozygous or homozygous (this last doesn’t apply to Overo, obviously).

Yes, especially because we know that the uterine environment plays some role in the distribution of white - not the location, it won’t change it from a blaze to, say, a sock - but it can absolutely affect how much white is on the face, or the leg. Look at the clones of Smart Little Lean - fairly widely varying degrees of face white. Others too - Top Gun went from low socks to tall ones

Do individual mares or stallions tend to reliably produce foals with “better” markings than other mares or stallions? I suppose no single mare has enough foals in her lifetime to give statistically meaningful data. But there must be stallions out there with 100+ offspring. People do advertise pinto/Paint stallions as “guaranteed to throw colour.” But even then the range of patterns they show for foals is quite varied.

“guaranteed to throw color” is true for ToTo horses. But many give that guarantee when there are only Overo patterns present, and that’s not true (but great for the MO if a foal comes out solid!).

But there are some like Sempatico who are pretty good at producing a similar pattern, and in his case, that’s a more minimally marked Tobi. There are also some that produce high white horses, so less desirable. The majority though are in the middle range of how much white, but how that’s expressed is hugely variable. I did know of a mare though, ToTo, whose foals were usually marked more like her, and IIRC she was roughly 50/50 white.

[QUOTE=Simkie;8244214]Jorene Downs had one years ago–foal by a homozygous tobiano came out without a STITCH of white on it, IIRC. DNA test came back as it should. I wonder if the info is still on her site?

Nope, but wayback still has it. (She does have a star and a little sock!)[/QUOTE]
Interesting! I wish I could remember when the actual gene for Tobiano was discovered, as opposed to just testing for the marker. I think it was after '02. I wonder how she’d test now?

But, we know it happens in minis (though really rare to be THAT Minimal) and they test Tobi with modern testing, so it’s certainly possible it happens in regular horses.

[camohn]

Tobiano: occasionally there is minimal expression, but it’s unusual. Usually if it’s there it’s obvious. In warmbloods it’s usually color linked to black based. You don’t see very many chestnut tobianos. Paints is a different story. Overos of various types usually expression is more marked on a chestnut base, more repressed on a black base.

[JB]

@camohn;8244486

In warmbloods it’s usually color linked to black based. You don’t see very many chestnut tobianos.

That’s only because Samber’s Tobi is linked to black. But he does have offspring where it crossed over, starting a new line of red-linkage.

But overseas, there are many more red-linked Tobianos. Solaris Sporthorses bred Umenno, who is out of a Samber mare, so lots of chestnut tobis through that line now.

There’s also James Bont, a red tobi Gelderlander, by the red tobi Unitas.

Paints is a different story. Overos of various types usually expression is more marked on a chestnut base, more repressed on a black base.

Yes, that’s the black suppression going on, and that’s regardless of breed, and only related to the overo and appaloosa patterns.