coat colour & creme gene question

[amy_b]

why are there no cremello/chestnut haflingers?!
also, does anybody know why in chestnut->palomino's the creme gene makes the mane and tail white, but in Bay->buckskin the mane stays dark?!

and finally, why are there no black/chestnut cleveland bays?!
(im sure there are 101 breeds that are the same but these one spring to mind)
thanks in advance brainboxes!!

 

[Loika]

Okay! I have looked into coat colours previously but maybe a bit rusty.

The Haflinger is a chestnut with the silver gene not a chestnut dilute(palomino), so doesn't carry the cremello gene so won't produce any creams, just chestnuts with flaxen manes and tails.

No idea why the mane and tail in a palomino should go pale and a buckskin remains dark. It may be that the cremello gene only interacts or strongly interacts with the red pigment not the black. Unfortunatly genes do not interact like paint, other mechanicisms occur, such as hormones, temperature and dominance/recessive/co-dominance. Usually "something" is dominant over "nothing", so a gene that codes for a product will be seen over a gene that blocks a pathway or breaksdown a product.

Not sure about the Cleveland bay but I expect given it's rarity(small population) and consistant outcomes of only bay horses that all pure breds are homozygous bay and black (as you can't have bay without the black gene to modify). The other one to look into is the fresian, chestnut horses do occur, although very rare in the pure bred population but the breed is prone to a range of inherited diseases, most likely caused by the selection for colour and "founder effect". Whilst breeding animals (not just horses) for purpose or colour/looks has its benifits, it is not without risk.

I hope this kind of helps a bit. There was a brilliant website available but I couldn't find it, sure there will be someone with some more information.

 

[Eluana]

Haflingers are chestnut with pangare and flaxen. They do not have the cream gene, which is why they don't have any dilute horses.

Cream affects pheomelanin, the red pigment, and has little to no affect on black pigment, if the horse has only one copy of the cream gene. When the horse has two, then the black pigment hair is affected as well as the red and the colour is double diluted.

There are no black/chestnut cleveland bays because of selective breeding and how the gene works - Bay is E/? A/?
Horses have two base colours - black and chestnut. All other colours come from modifier genes. What determines the base colour is the Extension gene.
‘E’ is what causes black pigment, eumelanin, in the hair, where as ‘e’ is what causes the red pigment - pheomelanin.
E is dominate over e, so you only need one copy for the colour to be black based.

The next gene is the Agouti gene, that controls the where the black pigment hair is distributed on the horses coat.
There are four alleles that affects this.
a is no affect (black)
At shows red at 'soft' areas (brown/dark bay)
A+ is wild bay (so small black points on knees and fetlock area)
A is bay.
In the order I've listed them in, the one after is dominate over it. A black horse is E/? a/a.
As I said before, Bay is E/? A/?.

What I'm getting at is, with the cleveland bay, they got the genes to E/E A/A, so the only option is bay.

ETA: Didn't see someone else had replied, think I've basically repeated what they've said

 

[amy_b]

thanks! interesting!!

 

[KarynK]

... and finally, why are there no black/chestnut cleveland bays?! .

It took a couple of hundred years to breed the chestnut out of them as a lot carried chestnut, and technically it could still happen, recessive genes are much harder to get rid of than dominants, its a bit like Grey in the Lippizanner, although Grey is a dominant not all of them are yet homozygous so the odd solid coloured horse pops out now and again, though that will get more rare until they are all homozygous, then they will all turn grey.

It's much easier to create a chestnut breed like the Suffolk Punch, because if you start with chestnuts all you can get are chestnuts!