So, exactly why do greys go lighter?

Ravenwood

Ravenwood

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For all these years I have just accepted that greys eventually end up "white" or flea bitten - I have had 6 greys in the past! (one named Ajax :rolleyes:) :eek:

But bays stay bays and chestnuts stay chestnut (obviously accepting the change in summer and winter coats)

So why do greys start off black/chestnut, change to dapple/steel and then eventually end up white/flea bitten in their dotage?

What is it in their make up that makes them fade with time when other colours stay the same?
 
Greys carry one or two coppies of the grey gene which is a dominent gene and it creates a depigmentation pattern of the original coat colour, it basically causes silvering of the hairs of the coat and it just keeps working until there is basically nothing left to turn grey!
It doesn't affect skin colour though, that always remains unchanged.

Why some turn white by the time they are 10 and some at 20 I dont know, I have no idea why the gene acts faster in some horses than in others x
 
It is a single mutated gene that is responsible that has now been isolated and it is the presence of that mutation that causes grey. All greys have the same mutation that can be traced back to a single common ancestor that lived thousands of years ago.

The gene is dominant so only one copy needs to be inherited for a horse to be grey. That means that it must have at least one grey parent. A breeding horse with one grey gene will pass it on to around 50% of it's offspring. If a horse has two copies and is used for breeding all it's offspring will be grey and those that have 2 copies will grey faster.

The appearance of grey dominates all colours in the horse, it is not actually a colour itself. The gene strips the colour from the hairs of a horse which will still have a proper colour gene hidden by the greying effect. The only colour it has no effect on is a dominant white horse, as that is born all white anyway so there is no colour to strip!

Unfortunately the gene is associated with the formation of melanoma's some of which can turn cancerous. The Grey gene has an effect on a type of stem cell which is thought to promote melanoma development in Grey horses, so there is a down side to this mutation.
 
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Just wanted to add that with flea bitten greys, something in the mechanism of depigmentation is lost enabling normal pigmentation to be reestablished. So the colour comes back.

Thats about as far as I can search my brain, I graduated back in 1996, so its getting harder to remember lol x
 
And then you get the "blood mark" mutation...

Dorey has had some of her brown spots all her life... but whereas a true grey would go grey and stay grey, some of Dor's grey hairs are now turning back to chestnut.

Theoretically, if she lived to an old old age, she'd be chestnut where most greys should be white.

ATM she's fleabitten grey with a few patches and a large area of roan!

Fascinating!
 
All horses have a base colour, this is either black or chestnut. If a horse has one black gene and one chestnut gene it will look black, as black is dominent over chestnut.

All other colours (eg bay) are due to modifier genes that change the base colour.
 
Interesting.

I had a grey (born chestnut) that at 10 still had some dappling, by 14 he was pure white but with a lot of chestnut 'fleabites' appearing on his neck and shoulders.
 
KarynK said:
It is a single mutated gene that is responsible that has now been isolated and it is the presence of that mutation that causes grey. All greys have the same mutation that can be traced back to a single common ancestor that lived thousands of years ago.

The gene is dominant so only one copy needs to be inherited for a horse to be grey. That means that it must have at least one grey parent. A breeding horse with one grey gene will pass it on to around 50% of it's offspring. If a horse has two copies and is used for breeding all it's offspring will be grey and those that have 2 copies will grey faster.

The appearance of grey dominates all colours in the horse, it is not actually a colour itself. The gene strips the colour from the hairs of a horse which will still have a proper colour gene hidden by the greying effect. The only colour it has no effect on is a dominant white horse, as that is born all white anyway so there is no colour to strip!

Unfortunately the gene is associated with the formation of melanoma's some of which can turn cancerous. The Grey gene has an effect on a type of stem cell which is thought to promote melanoma development in Grey horses, so there is a down side to this mutation.
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Does anyone know the mechanism by which it strips the colour out. I am a molecular biologist by trade and am now very interested! I had never thought properly about how this would work before and had always assumed co-dominance was somehow responsible.


Also, two copies of the gene for grey gives you??! Grey again but then there is no base colour to be stripped. Obviously grey parent plus grey parent has a perfectly good chance of passing on double grey copies. Hmmmm
 
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The Swedish team that located the mutation think that the gene stimulates growth of melanocytes, and very much like happens in humans but much more rapid there is a premature loss of the melanocyte stem cells needed for hair pigmentation, interestingly with the gene the mutation also promotes the over production of some of the melanocytes causing skin pigmentation, hence skin pigmentation is not lost. It also accelerates other stem cells that produce the melanomas, so good and bad!!!

The mutation does not change any protein structure but it affects the genetic regulation of two genes, Grey horses carry an extra copy of a segment located in one of these genes.
 
You don't, by any chance at all, have a link to the papers do you? Are they published. I can search by author if you know that? Really intrigued. Because it's horses for a change instead of boring people! Don't worry if not and thanks for answering my questions :)
 
KarynK said:
A breeding horse with one grey gene will pass it on to around 50% of it's offspring.
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Sorry to pick, but surely you mean each offspring of a heterozygous grey horse has a 50% (ish) chance of being born with the grey gene? So, technically, a grey bred only to solid coloured horses *could* go its whole breeding life without ever producing a grey horse. If someone wants to breed a grey horse they need to make sure at least one parent is homozygous. And because I have a thing about probability. ;)

There was a paper a few years ago now (I want to say it was Dutch but I honestly can't remember) effectively positing "greyness" as a "disease". It got a lot of people stirred up on the internet forums (mostly on the old subject of whether *all* grey horses get melanomas) but otherwise clearly wasn't a popular theory. ;)
 
TarrSteps said:
Sorry to pick, but surely you mean each offspring of a heterozygous grey horse has a 50% (ish) chance of being born with the grey gene? So, technically, a grey bred only to solid coloured horses *could* go its whole breeding life without ever producing a grey horse. If someone wants to breed a grey horse they need to make sure at least one parent is homozygous.
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As the owner of a grey stallion who IS heterozygous, I can assure you it's VERY unlikely! Even from non-grey mares, at LEAST 50% of Raj's foals are grey. Foals out of heterozygous grey mares are almost inevitably grey! (I had 7 foals from one grey mare by Raj - just one of them is bay! With one bay mare, of 5 foals, 3 were grey, 1 chestnut and one bay. Another bay mare, 5 foals - ONE bay, the rest gray. I could detail more,butyou get the picture. So yes, it is theoretically possible - but very unlikely.
 
Foals by a hetro grey stallion out of a hetro grey mare have a 25% chance of being non grey....far from "almost inevitably grey"

...they also have a 25% chance of being homo grey and 50% of hetro grey.

You really need to look beyond your statisticly tiny sample for any valuable conclusions!
 
gekko said:
Foals by a hetro grey stallion out of a hetro grey mare have a 25% chance of being non grey....far from "almost inevitably grey"

...they also have a 25% chance of being homo grey and 50% of hetro grey.

You really need to look beyond your statisticly tiny sample for any valuable conclusions!
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This, statistically is absolutely right. I just drew the punnett square for it (what a sad girl I am). As with all probabilities you need a huge sample set to get an accurate idea of what is going on in real life but assuming grey is completely dominant to all non grey colourings then genetically speaking this are the only probablities which work!
 
TarrSteps said:
Sorry to pick, but surely you mean each offspring of a heterozygous grey horse has a 50% (ish) chance of being born with the grey gene?...

There was a paper a few years ago now... effectively positing "greyness" as a "disease". It got a lot of people stirred up on the internet forums (mostly on the old subject of whether *all* grey horses get melanomas) but otherwise clearly wasn't a popular theory. ;)
Click to expand...

That's precisely why I said "around", it's possible for a horse who only has a few foals but for a stallion covering a lot of mares it will not happen as the closer you get to 100 foals then the ratio will balance.

The current research project isolating the gene estimated 75% of greys had melanomas but an Australian study by post mortem found 100% had them, some were concealed internally. Since some melanomas become cancerous and others cause problems in later life then yes because of its action in promoting melanoma's grey can cause disease.

Yes grey is dominant by it's action over all coat colours except dominant white. But as said above some horses appear to be able to partially counteract the effect in localised groups of hairs or patches.

The really interesting fact is that Grey has been perpetrated by humans from a single animal that mutated. With other mutations in the horse like PSSM, the horse as a species is prone to the "disease" but the actual mutation effect is different between breeds. Roan horses are also thought to emanate from different mutations as we now know are dominant whites, yet all greys have the same mutation.
 
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