The Colors of Life

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Melanin...

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CMhorses
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Melanin...
So for whatever reason, I've been reading like a madman about melanin production, and it got me thinking about how the different shades of colors, like bay or brown for example, are probably explained by melanin production (obviously). The way a geneticist described possible human hair color production was that there was 8 different genes that turn off or on meleanin production. Eight was used to just simplify the concept, so 4 from each parent. So someone with blond hair would only have none or 1 of the 8 genes set to "on", someone with dark brown would have maybe 6 of 8 turned on. They also mentioned about the mixture of eumelanin and pheomelanin production and how you can have a partially working MC1R gene and still have some pheomelanin converted into eumelanin, but a buildup of pheomelanin still occurs, so you could have brown hair with a red tint to it instead of being a straight redhed, which was when you had two non working MC1R genes. Then I read about brown and black eumelanin, and that threw me for a loop considering they are basically the same, the only difference that I could find was that black eumelanin was more oxidized while brown was stopped short in the production process, and less oxidized and slightly different shaped. I could find nothing on the why this happens. So, back to horses, it may be obvious to everyone else, but I feel like I had a mini breakthrough in thinking about bay. The melanin production in the points/mane/tail is normal eumelanin while the color on the body could be a mixture of eumelanin and pheomelanin, with darker bays having more eumelanin and ligher more red bays having more pheomelanin. There is probably something that controls whether black or brown eumelanin is produced, and it seems like in brown horses, they have brown eumelanin and black eumelanin as well as a little pheomelanin. So, the ones that are really light, almost like a regular bay seem to be usually really brown and not very red, so that, to me, means they are producing brown eumelanin and probably some amounts of pheomelanin, but in general they are not producing as much pigment in general. I'm sure it can be simplified; a light brown At horse has only 5 genes turned on, with one of those 5 not working, so making red, while a dark brown horse has all 8 genes turned on but 1 is making brown and 1 making red. In chestnuts, I didn't get as far, seems like they have two broken or turned off MC1R genes, so they produce only pheomelanin, but the amount of pigment they produce varies to give us liver chestnuts who could have all 8 pigment genes on, to lighter chestnuts that only have 4 or so turned on. I think this could also partially explain how red based horses and even Ee horses generally have more white from white patterns than EE horses.Red looked like it needed more molecules to create than black, so its possible that if there was a shortage of molecules, there would be more room for white areas. I know this was quite long and probably doesn't make hardly any since, so if anyone knows what I'm trying to talk about feel free to correct me. :bounce
Threnody
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Thanks for the post, really

Thanks for the post, really interesting. I think in the case of sooty in horses that it causes eumelanin to activate even though the two MC1R genes are deactivated. It would be interesting if 'shade' genes for melanin interaction ever get isolated.

CMhorses
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yes i was thinking about

yes i was thinking about sooty and i agree with you, with bend or spots i was thinking that was more somatic because its like a small area only got turned on while other parts of the body make their normal color

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Dogrose
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I wouldn't try to complicate

I wouldn't try to complicate things by bringing human hair colour genetics into the mix. Horses do not have a brown melanin mutation, they only produce black or red, though both these can vary in intensity it is most probably from minor modifying genes.
Bay is agouti which basically means the production of black melanin is switched to phaeomelanin for a period of time during hair growth, variations in this timing cause different proportions of yellow to black and can affect the overall look of the animal. This switching does not occur on the points and long hair of the horse. With the self mutation, aa, the switch mechanism is disrupted and the horse is black all over, in the At mutation the switch is restricted over a larger area of the coat but not completely.
The Extension gene which governs whether a horse is black based or red/yellow based has quite a few mutations in other mammal species and mutations on this gene can cause different types of sooty on red or darker shading on agouti in those species.

[color=#804000][i]I bought me a horse twas called a grey mare
Grey mane and grey tail and green stripe on her back
Grey mane and grey tail and green stripe on her back
Weren't a hair upon her that was not coal black[/i][/color]

CMhorses
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I actually couldn't seem to

I actually couldn't seem to find hardly any info specifically related to horses, only on humans, mice, birds and like amphibians. Thanks for clearing some things up!

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