Tobiano Suppression - A Study

[Silverine]

I'm not sure how much help I'll be but I'll give it a shot.

For suppression as I have it modelled, there is nothing that will block face white but allow leg white. It'll all depend on which white genes the foal inherits from its parents.

It looks like you're working with a mix that is mostly Tarpan based with some Prze and Shetland thrown in. Tarpans will be mostly B-type suppression - no body white, but will show white on face and legs. It is possible, though unconfirmed, that Tarpans also carry A-type that blocks white everywhere. But it's much more likely that your Tarpans are throwing Bs.

Przewalskis only have A-type. They completely suppress all white expressions. This means that any first-generation Exmoors will have 0 white on them.

Since Exmoors are a Tarpan x Prze cross, any first generation specimens should be AB for suppression. This means they won't show white, but have the potential for leg and face white in their offspring. If you breed two first-gens together you have a 25% chance of the foal being capable of showing white, and a 75% chance of suppression with 25% being homozygous for suppression (none of their foals could show white).

Then there's Shetlands. Shetlands do display body white. This means that they have type-C suppression, which is to say none at all. If they have tobi, it will be all over. As far as I know, AC Shetlands do not carry type A or type B, and so will only ever pass on type C.

On to your horses:

Little Wiggle is a first-generation Exmoor. This means he could possibly have a tobi gene, but we won't know because he should be AB suppression - he won't show any white himself, but his offspring could. The same goes for Luminescent Effect.

The mares are all Tarpan x Shetland. That means that they are all BC suppression - they can only show leg and face white, but have the potential for foals with body white.

Forgive me if I'm wrong, but it seems that you outcrossed to Shetlands to increase the white content? If that is the case, I do not believe they will be overly helpful. Shetlands would be great if you want to put white onto the body, or to increase the white that is on the body, but they're not really known for face white. You're much more likely to end up with a "slipped" tobiano - a B-type suppressed horse that should have body white, but the white "slips" down to the leg because of the suppression. I believe a better strategy would be to breed together Tarpans with face white, or to add in Belgians, Forests, or Turks with face white. Using those three breeds will also eliminate the chance of foals with body white as all have type-B suppression.

[Sunpath]

Thank you so much for your extensive reply, it was a very insightful read!

It was mainly the fact that I kept getting leg white but no face white at all despite the mares all having face white that threw me off a bit. In my mind, a foal that can display leg white should also be able to display face white, and with that many mares covered at least 10x each I felt like at least one should pop a foal that has some white on their head but that didn't happen. Which made me wonder why that is. Was I just extremely unlucky? Or is leg white in some way dominant to face white? But then again there's plenty of horses in game that display both so I didn't manage to wrap my head around that either.

The shetlands added in was mostly an experiment to be honest. I usually use belgians, tarpans or forest horse. I've looked for turks in the AC with face white but actually never found one.

[Fendy]

Sorry to give this a topic a kick. But after a lot of breeding with my Quarter Horses, I have noticed the following; There are obviously different “groups” of genes separate from each other that allow certain whites to be bred. What I am referring to by that is different groups of types of tobiano.

For example, my Endurance horses have mainly white over the head and neck, including the two front legs - this is completely dominant in my line and does not change unless I add new blood (and thus perhaps new genes). Now I already have 1000+ foals going on with my Quarter project and am lucky to breed about 90% white, excluding one specific leg that is still missing.

So after adding yet another new blood with horses from the AC, then after 2-3 generations of breeding, suddenly I do manage to get horses with more white on that leg that was always missing white. Making me a 99.9% sure tobiano genes are divided into groups on the horse's body, and when a horse lacks a certain gene then white on that spot is just impossible to get.

After I crossed these foals with white leg with the almost completely white horses they did show certain white, but not all of it. But eventually they did carry these genes; and just passed this on after 1-2 generations. This really makes it more than clear to myself that there are certain groups in terms of tobiano genes that you need to get a completely white horse. Eventually they all pass this on after 1-2-3 generations of selection as well. If you miss a gene then you can immediately see where white starts to be missing.

[Silverine]

Yes, it has been verified that there are different alleles for different areas of white, and to get full white you need all of them. This is in addition to the suppression that I am looking at here. The suppression will prevent white expression, even if you have the genes for it. It is why you will never get white on a foal from an AC Przewalski or Arabian, even if the parent is homozygous.

Lp is known to have the same allele mapping behavior as tobiano. I haven't mapped tobiano, but here is an approximate Lp map that I drew up years and years ago:

[MulberryGrove]

Very interesting!!

My Tarpan x Shetland corroberates this i think, he has only a bit of sock

Both parents from the AC, his mom the shetland has a bit of Tobiano on her ribcage

Lugh

[Argent]

Can this be pinned