Why are homo black horses not really?
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Re: Why are homo black horses not really?
But if that is the case then surely a cremello must look the same as a palomino and a perlino must look like a bay as it's just a case of 2 of the same gene, and we all know that is not the case ;) Or for that matter a homo tobi frequently has paw prints whereas a hetero tobi does not - surely is it not possible then for a homo black to be slightly different??
Re: Why are homo black horses not really?
http://andalusiansdemythos.com/conquist…" onclick="window.open(this.href);return false; he looks pretty black to me. And if you look through the gallery you'll see that depending on time of year, and light source, his coat shins differently. For me that's just the sign of a healthy coat.
There could be many things effecting the shade of a horses coat, nutrition and sun is a big factor.
The Freisian breed is a good example. I believe aside from a hand full of horses, the breed is EE. And if you google search the images, you'll see all kinds of shade expressions. And I know there are a few owners out there who's freisians grow in their winter coats in this false bay.
Re: Why are homo black horses not really?
[quote="Hey What The"]But if that is the case then surely a cremello must look the same as a palomino and a perlino must look like a bay as it's just a case of 2 of the same gene, and we all know that is not the case ;) Or for that matter a homo tobi frequently has paw prints whereas a hetero tobi does not - surely is it not possible then for a homo black to be slightly different??[/quote]
They are different genes! Only takes one black gene to make a black, so no it doesn't get any more (or less) black with another one. I've seem many different shades of black in both heterozygous and homozygous.
Re: Why are homo black horses not really?
[quote]But if that is the case then surely a cremello must look the same as a palomino and a perlino must look like a bay as it's just a case of 2 of the same gene, and we all know that is not the case Or for that matter a homo tobi frequently has paw prints whereas a hetero tobi does not - surely is it not possible then for a homo black to be slightly different??[/quote]
I would like to add that extension is a simple dominant gene. Meaning that only one copy is needed for full expression. Cream is what is known as an incomplete dominant. Meaning that expression will be different depending on whether one or two copies are present.
Re: Why are homo black horses not really?
On a molecular level, what the different alleles do is affect the amount of protein produced in that gene. For extension, having one dominant allele is able to produce more than enough protein that you get black phenotype. When you have two copies of you get even more of the protein produced at that gene, but you still only need a certain amount to express it fully. In other words, an excess of protein is produced with two dominant alleles even though you only need a smaller amount to trigger the phenotype.
To say it another way, say that for a melanocyte to produce black pigment, it needs to be signalled by 5 copies of a protein. For this example, let's say that one copy of E causes 8 copies of the protein to be made. You end up with the 5 you need to make black pigment, with 3 extra. If you carry two copies of E, you would make 16 copies of the protein, but you still only need 5 to have the melanocyte make black pigment. You just made a lot of extra protein. The extra protein produced does not affect the amount of black pigment made.
Re: Why are homo black horses not really?
[quote="accphotography"]Tobi is also considered a somewhat incomplete dominant as well.[/quote]
Really?! How do they figure that? It's not like they get 'more' tobi with two??
As far as the paw prints go, I've always wondered if that's not something that can link with tobi, and shows up better when two of them. As the paw prints seem to run in families, and they obviously aren't on all homozygous tobi's.
Re: Why are homo black horses not really?
[quote="accphotography"]Actually the researcher that discovered the tobiano mutation DOES feel they get more expression in homozygotes. She also feels homozygotes get more face white. :D[/quote]
Nuh I definitely don't agree with that. In fact from the same breeding I've had the homozygotes with less expression before (and more), and definitely not more face white either. The more face white is more connected with the red or black (depending on horse) and wether tobi is there or not. Not wether there is one or two tobi genes. (to clarify, the shetlands only show their face white when tobi is there, not saying it's necessarily the tobi causing it, but it does need at least one tobi gene there to express for some reason, I thought maybe the enabling white expression gene is linked to tobi somehow...)
I'm going to keep an eye on this now, but at this stage I've seen nothing to support homozygous tobi's with more white. The expression just seems to have the normal range of more or less :?
Re: Why are homo black horses not really?
But do the homozygotes that have less white than the heterozygotes have a suppressor?... like this one...
http://i173.photobucket.com/albums/w65/…" onclick="window.open(this.href);return false;
Don't shoot the messenger though. I'm not saying I believe this, I'm saying this is what the researcher found when doing the tobi study.
Re: Why are homo black horses not really?
I think the researchers may have mixed up the possibility of partial dominant white patterns present besides tobi. Likely due to the old issue of we "won't know until everything is testable" :P Don't worry ACC no attacking the messenger here.
The pawprints seem almost like tobi is attempting to suppress itself when homozygous. Obviously other suppressors can cause a pawprint-like phenotype.
Re: Why are homo black horses not really?
Extension zygosity (if the horse is E_) has no effect on the horse's phenotype.