There have been some great explanations about colored/painted TB genetic here…special thanks to JB, but I have another scenario.
We have 5 Puchi’s Rambo (Puchilingui/DW #5 gene) mares…One pure white/bay spot on neck, three loud/spotted/roany overos (I know that term isn’t favored, but it does describe what we have. What (theoretically) would we get breeding the loud mares to a heterozygous tobiano stallion. Would the tobiano be dominant over the DW5 gene or vice versa…or is it a 50/50 shot???
You’d have a 50/50 shot at the sire passing tobiano, which is completely independent of your chances that the mares pass their color. I don’t see why tobiano and W5 would be mutually exclusive; there is no need for one to be “dominant” over the other, it’s entirely possible that the foal could inherit both color pattern genes.
Well tobiano is dominant in that if it’s there you see it. So 50/50 on the tobi. In very rare cases there are minimally expressed tobianos…but it " almost never" happens. 99% of the time if it’s there it’s obvious. The DW on the other hand is multi gene influenced, so its expression ( not its heritability , which is still 50/50) can be masked, thus the crop out overos. But, since they are separate genes, one isn’t dominant over the other. You could get solid, Overo, tovero or tobiano …
Yes, 50/50 of passing the Tobi.
It’s possible for the 2 KIT mutations to boost each other, resulting in very loud (ie more white) foals.
Tobiano and these DWs are KIT mutations, so while not mutually exclusive, they are “homozygous mutually” exclusive, meaning (as far as we know) you can’t have ToTo and some DW. You can’t have To and W5 and W20. But you can have, in this case, To and W5.
Because KIT is linked to Extension, so there is the issue of having solid red-based foals and W5 black-based foals, (or the other way around) for example, just like there’s the link between Tobi and Extension, so there is some link to the color and pattern combination.
Without going back and looking at the mares and their foals again, I couldn’t tell you if their W is linked to E or e (or if it’s even a known fact, since if it’s linked to e it can be hard to figure out), so I can’t predict that part.
It might be possible to figure out the stallion’s To-E linkage based on his parents, or his offspring if we know the dams’ color/pattern as well.
Thanks!!! You “guys” really know your stuff!! I just got really bummed this year with NO spots!! GORGEOUS babies…huge, correct and sweet, but no spots!! The 3/4 TB-ISH filly has the most white…stockings to knees and hocks and a pretty blaze. The 7/8 TB ISH colt has the odd stockings and question mark blaze. All have white chins…FWIW!! I’m seriously considering a nice, sporty pinto stud, but I’ve never crossed DW with tobie.
The problem is that Tobi by itself has SUCH a huge range of expression, from low socks (nearly all minis, who don’t really count 
) to the white horse with a colored head, which makes is really, really difficult to know how much DW and Tobi play together. We know that Splash and Frame together tend to exaggerate the presence of white, which is an much easier thing to quantify.
All we know for sure with this Toto stallion is the 50% chance each foal will be Tobi. How much white they have is all up in the air.
[QUOTE=JB;8000913]
The problem is that Tobi by itself has SUCH a huge range of expression, from low socks (nearly all minis, who don’t really count ) to the white horse with a colored head, which makes is really, really difficult to know how much DW and Tobi play together. We know that Splash and Frame together tend to exaggerate the presence of white, which is an much easier thing to quantify.
All we know for sure with this Toto stallion is the 50% chance each foal will be Tobi. How much white they have is all up in the air.[/QUOTE]
This was my concern when we started breeding painted TB’s and Sport Horses 20+ years ago. I love “most” patterns, but some are really gross looking!! I’m not fond of bald faces or medicine hats, but I guess that’s the chance you take with color. ALL of our mares have dark around their eyes and the tobies I’ve been considering are mostly minimum white. Guess we’ll just have to see. Thanks for the “facts”!!
I stand corrected - there is a ToToW4 horse out there, which means there can be at least some homozygous crossover (ie homozygous for one thing on KIT, then the addition of something else on KIT), though it’s quite rare. So far there is nothing tested for ToToRn for example. The thing with Tobiano is it’s “near” a gene, not exactly on that gene, so there is a very small chance - very small - that a crossover can occur and you can get something like this ToToW4. But that’s even more rare than the 7% crossover you get with the To-E link.
[QUOTE=JB;8001689]
I stand corrected - there is a ToToW4 horse out there, which means there can be at least some homozygous crossover (ie homozygous for one thing on KIT, then the addition of something else on KIT), though it’s quite rare. So far there is nothing tested for ToToRn for example. The thing with Tobiano is it’s “near” a gene, not exactly on that gene, so there is a very small chance - very small - that a crossover can occur and you can get something like this ToToW4. But that’s even more rare than the 7% crossover you get with the To-E link.[/QUOTE]
NOW you’ve totally lost me!!!
LOL, sorry 
Most “things” are on a specific gene. Black/red is on the Extension gene - not beside it, not close to it, ON it. Same with Agouti.
For a while, dun was only determined by look at a marker close to some gene. Now they know exactly which gene.
Each gene has 2 settings - on or off. The “on” portion might only be a single thing - extension is either “off” as e, or “on” as E. Period.
But the “on” portion might have multiple values. Agouti is off with a, but is “on” with either A (bay) or At (brown), or a theorized A+ (wild bay). Cream is either off, or “on” with Cr (cream), or with Prl (pearl). That means a horse cannot be homozygous for cream and be a pearl carrier - can’t be CrCrPrl.
But with Tobiano, while it’s still a reliable test (unlike dun which had some issues which is why testing strongly requested a picture of the parents), still only looks at something that’s (very) close to KIT. It’s not ON KIT.
So, while it’s close enough that there shouldn’t be anything else there if the horse is ToTo, it’s far enough that an anomaly could occur and there be 3 “on” values present. And KIT mutates * a lot* so there are more “things” that could tag into a ToTo situation.
It seems all but impossible that the 3rd value could be Roan because of the location, and so far there aren’t any of these, but because Tobiano isn’t ON a gene, it’s still possible, however remote. It’s good enough to say at this point that it can’t happen - sort of like “there are so few Roan TB lines and so few individuals, you might as well say Roan doesn’t exist in TBs”
