I just got back from an equine genetics conference in Tahoe City (unfortunately a day early, as a massive fire started about a mile from our conference center this afternoon and we all had to be evacuated. If you haven't seen it on the news, you can check it out...35 acres so far. We packed like crazy bunnies and flew out of there with the baby!). Anyway, I thought I'd share some of the coat color highlights from this meeting. There were representatives from all the major labs around the world and there is so much exciting stuff going on in this field now...it's amazing how far we've come in the last ten years. Each of these little nuggets probably warrants its own thread for discussion, and anyone is welcome to start a new one for any of them. I just didn't feel like making a bunch of threads tonight...way too exhausted!
Gray: Yes, they have the mutation! The Swedish group finally presented their results! It was fascinating, because gray is actually not a simple base pair mutation, like most of the coat colors. It is actually caused by a large duplication of sequence in an intron of the "gray gene". The paper is in press, so no test for a while. But they found some really interesting things when they tested 700 gray horses:
1. Homozygous grays go gray faster than heterozygotes.
2. Heterozygous grays have a much higher incidence of speckling (also called flea-bitten gray).
3. Homozygous grays have a much higher incidence of melanomas.
4. Homozygous grays have a much higher incidence of vitiligo.
5. And this is the crazy part...horses that are "aa" at agouti have a much higher chance of getting melanomas than horses that are AA or Aa.
Most of these finding are due to the way that the gray mutation works...the mutation causes a hyperproliferation of melanocytes (which collect as melanomas), but that leaves fewer melanocytes for the hair follicles, causing the horse to progressively gray with age. This is all kind of paraphrased, as I'm just going off the notes I took. The paper will be much more informative.
Okay, next...the debate about dominant white can finally be laid to rest! The Swiss group has identified the dominant white mutation! It is a single base pair change in the KIT gene (ah KIT, responsible for so many depigmentation problems). They had photos of horses tested positive for the mutation...and these horses were NOT max sabinos. They were white, sometimes with some skin pigmentation that you could see, but none in the coat. All of the white horses tested heterozygous for the mutation. Homozygotes, as suspected by breeding trials, are not viable. They mentioned several breeds, I think, but the picture I remember most vividly was from a Franches-Montagnes horse. They had previously mapped dominant white to KIT in 2004, I think...but now they actually have the mutation and can test horses for it. It is not always fully penetrant, leading some to the incorrect conclusion that the horses were actually sabino.
Dun: UC Davis continues to narrow down the dun gene. While they haven't found the mutation yet, they now have the region narrowed to two candidate genes. They're in the process of sequencing them for mutations. Hopefully that will go well and dun will be found soon.
Another group attempted to map splash, but was not really successful. It was a bummer.
There were so many other great findings (not coat color related). There was work on reproductive traits, the MHC complex (immunity), recurrent airway obstruction, polysaccharide storage myopathy (Minnesota found the gene for that disease and has the mutation), more work on HERDA, dwarfism in Fresians, more work on the genome sequence, cerebellar abiotrophy...it was really great. Watch for the papers on the two coat colors above...they're in press!