genetics of chocolate brown horses?

[Susara]

What genetics are behind dark/chocolate brown horses? That is, horses that are dark (not chestnut) all over, including mane & tail. Are they just a particularly dark version of liver chestnut? In fact, am I correct that liver chestnut is the result of a darkening gene, comparible to the dilution genes? Chev has mentioned that we don't really understand the genetics of dark bay yet - would this be related to my question?

[virtuallyhorses]

Well I'm not sure what you call a dark\choc horse however I'm guessing it is the seal brown (or plain brown) horse that you are referring to. Traditionally this has always been thought to be genetically a black EE horse. However there is some research that believes that seal brown may be a type of bay with the A (Agouti) gene. As with so many colour questions - lots of theory and not much fact I'm afraid.

[chev]

As Viv says, there are lots of theories and very few hard facts. Chocolate brown horses could be the result of several things; black with a dilute gene (black with cream sometimes gives a really dark brown horse - Ambatt has a lovely example), a very dark liver chestnut (some of whom darken as they age, some of whom don't!), or a variant of bay, or a black that's faded.

Seal brown horses (that is near black horses with pale muzzles) have tested positive for agouti, which suggests there is a type of agouti that cause that appearance.

There is no explanation of liver chestnut really; one theory was that it was the result of chestnut + sooty (sooty causes black hair to be distributed over the top half of the body - as in most dark bays) but since liver chestnuts have no black pigment and don't have the same distribution pattern of dark hair as horses that carry sooty (liver chestnuts are usually uniformly dark) it seems unlikely.

[Susara]

wow, I find it surprising that we know so little about the genetics. Dark bays are common, and we don't know how they work?

With dark/chocolate brown I simply meant a darker brown than what one would typically call a chestnut - only going by looks. I'm usually not sure what the official terms of colours are so I use whatever I think should describe what I see :)

At the stable yard we have a roan mare (definitely roan: no roaning on face or lower legs, no progression over the years, etc) but the unroaned bits are milk chocolate brown - too brown to be chestnut. So I was wondering what the base colours would be that the roaning is working on. And then I noticed there were lots of dark brown horses around that would be dark bays except everything is brown.

[chev]

We don't know how dark bays work *for sure* yet.

So far, the gentics we know about include the Extension gene (dictates whether a horse carries black or red pigment); the agouti gene (we know it restricts black pigment, have identified the gene itself, but not exactly how many variants there are); the cream gene; and sabino1. Those four are all genes we can identify.

We also know about tobiano, and roughly how it works; the gene itself has not yet been identified, but we have identified certain protein markers associated with the gene. We can identify most carriers of lethal white overo syndrome.

But a lot of the genetics of shades of colour (like dark bay and flaxen chestnut) are still in the realms of theory. The theory is sound; especially in the case of the sooty modifier causing dark bay horses, but until a gene is mapped out and identified as sooty, and it's hereditary explained, all that will remain theory.

Because we understand a lot of how genetics work, we can usually theorise failry accurately.

Milk chocolate brown is not neccessarily too dark to be chestnut. If it's not black hair, then the horse is almost certainly a form of chestnut. Two of my liver chestnut mares are almost the colour of plain chocolate - but still definitely chestnut based.

Chestnut can be a huge range of shades, from the lightest ginger right through to the darkest chocolate. Chestnut simply means there will be no black pigment, although some chestnuts are so dark that they can appear to have black pigment. It's sometimes only on close examination that it becomes clear it's not really black. We currently do not know what gene or combination of genes dicatates shade.

The other possibility is, as I said, that the base is a dilute black - unlikely to be faded black in this case since that would change with the seasons.

This stallion is liver chestnut - gives you an idea of just how dark a chestnut can be.... :)

[Susara]

Just re-read my previous post on this thread, realised it may come across as quite snotty - didn't mean it that way at all! :-)

I find genetics absolutely facinating. How they analyze the hereditary patterns and decude from that what the genes could be that would explain the observed patterns Then they can go look for them. It's like a mathematical puzzle. Really cool :-) Makes me wish I'd gone into biology rather than IT...

[Angel2]

My friend has a near TB that she describes as chocolate dun. He is milk chocolate coloured but with a dun ish muzzel and a brown mane and tail lightening to cream ish on the ends. He does not have an eel stripe or any signs of stripes on his legs. His mother previously had a palomino so I assume must be carrying a cream gene, would this make him a buckskin?

[chev]

Susara - you didn't come across as snotty at all, don't worry! :)

Angel2 - what colour is the horse's mother herself? Any idea what colour his sire is? What colour was the palomino foal's sire?

Buckskins have black points, so unless there's something else going on there he's unlikely to be buckskin. He could be a cream dilute of some type - don't think all palominos are cream or gold! Some are very chocolatey indeed... and manes and tails can be anywhere from near white to quite dark grey in colour.

This is Jula Mystical Lady (http://www.julastud.com/indexm.htm) (first pony pictured) - and she is palomino :D

[Angel2]

Chev, will get you a picture later as I drive them to their lesson at RDA this afternoon and find out somemore about his breeding for you. Thanks for your help, Viv will be so pleased.

[Angel2]

Here he is, his mother was bay possibly with roan markings by Master Spiritus, his father is Lord of Arabia who is also bay. His mother had a lighter version of him when put to a palomino - he has grown a bit of an eel stripe as he has gone cat hairy!
http://i24.photobucket.com/albums/c33/spikeselby/horsesdogsandgarden006.jpg
http://i24.photobucket.com/albums/c33/spikeselby/horsesdogsandgarden004.jpg
http://i24.photobucket.com/albums/c33/spikeselby/90e1b200.jpg
sorry, forgot to rotate the pics

[ambatt]

He is quite chocolatey! he also appears to have pangare markings (mealy nose and a bit around his eye.) It is very much like the primitive dun colouration found in Exmoors.

I have to agree that he is a very different colour - my Icelandic is a rich cocoa brown and she has the same slight eel strip.

Definitely a case for Chev to puzzle over!
(He is lovely BTW)

[Angel2]

Chev, any ideas??