Double Roans

Okay, so since I'm a genetics nerd, I'm a little confused as to why there are double roans in game. As far as I knew, breeding roan x roan = 25% non-roan, 50% roan, and 25% lethal white. This would be similar to double overo. Strangely, double overo doesn't exist in game, whereas double roan does. Is the double roan just coded in as a more white variant of roan? -squints-

I don't believe double roan is lethal. Turns out people used to think it was lethal, but more recent studies conclusively show it isn't.
Source1 & Source2

Last edited on 2016-02-19 at 07:13:09 by UlyssesBlue

I think there is debate still among researchers on the topic.

but recent molecular evidence is leaning toward the idea that RnRn is non-lethal.

It is hard to find any research out there that doesn't lead back to that study; personally I need more evidence and research before I pick one side or the other.

This is a very interesting topic. I've been reading a bit more, and apparently one theory is that since roan is on the KIT locus (like dominant white) it's possible there are multiple roan genes, some of which are homozygous lethal. Until there's a direct genetic test for roan (currently it's an indirect test) we won't know for certain.

Good point, UlyssesBlue. There's the Catch a Bird mutation roan, for instance. He was a reverse or white brindle (no roan in pedigree) and his foals were roan. So it depends on which roan you're talking about and there are at least two.

My theory for CaB is that he may have had a mutated rabicano gene (which Thoroughbreds do have, as they don't have roan). It's hard to see in some photos, but he did have the typical rabicano skunk tail, and some of his roan offspring also had skunk tail along with ribbing in the roan along their barrels. Classic rabicano.

It is believed that rabicano and roan may be closely related (and rabicano may also be on or very near the KIT locus). It is possible that if CaB was a rabicano mutant that the already broken gene could have mutated more in the offspring, producing rabicano-factored, true roan foals.

On roan and white. It is possible that there are multiple allele variants of roan just like there are for white, splash, and sabino to name a few. White (previously known as dominant white) has been discovered to be not homozygous lethal in some families.

Very interesting stuff. Also another intriguing TB is Oxbow. He LOOKS roan and his parents are pretty normal looking bays with average white for a non-patterned horse.
http://www.bloodhorse.com/stallion-register/stallions/166890/oxbow

I lied.. I had forgot his dam actually has an over spilling of white down her muzzle side/chin(almost like very minimal splash) but her feet are low white. Sire is nearly solid save a small star.

Last edited on 2016-02-20 at 00:03:04 by Årty- Tekes!

It's actually a misconception that all white markings come from white patterning genes, so a bit of chin white with short socks doesn't necessarily mean anything in regards to pinto patterning. Oxbow has some kind of odd roaning thing going on, but that's completely different from roan. Neither parents are roan, or grey (though a grandsire is grey, but that means nothing since it can't hide for a generation) and they don't appear to be rabicano from what I see. I've seen plenty of non-roan horses from non-roan parents with white hair anomalies. It's just something that pops up.

Unrelated to original to a degree, but... Does anyone here love White Horse Production's genetic pages? I know that's one of my go-to information spots at this point. Manchado still fascinates me. I hope they eventually figure out if it's environmental, a rare recessive, a new mutation, etc. So neat.

They are a great information source, though I don't know if they have recently updated anything.

Color Genetics is a good site. They have a lot of images for the different colors/patterns. Most of the horses listed have been color tested, as well.

Ooooh. Thank you, Kuk. -makes grabby hands- Well, I know what I'm going to be reading for the next...forever. -absorbs genetics articles-