homozygous ??

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Which in my way of thinking makes black - E - dominant. Obviously agouti is dominant too, but that is something happening to the colour rather than a colour itself??? Or am I just being simple

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I missed this - yep, you're being simple!

Whether a horse is black is actually governed by the agouti gene, although they must have the extension gene present too. If a horse has a dominant copy of the agouti gene in the presence of extension, then they will be bay. In order to be black, they must only carry the recessive form of the agouti gene, along with extension.

If they only have the recessive variation of extension, they will be chestnut regardless of their agouti status.
 
I am sticking with my its as clear as mud policy!
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Well except the Tobiano bit, if the horse has the Tobiano gene it will be coloured.
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Thanks Ashbank. So I have a black mare whos mother and grandmother are both black. Then her sire (De Niro), grand-sire (Hohenstein) and great-grand sire (Rubinstein) are all black also. Do you think it would be worth my while getting the mare tested, then if she did not carry the red factor I could put her to any stallion and be guaranteed either a bay or black??
 
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Do you think it would be worth my while getting the mare tested, then if she did not carry the red factor I could put her to any stallion and be guaranteed either a bay or black??

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Definitely worth it, especially if you want to avoid chestnut! I have tested most of my mares, and as it happens I have four homozygous black mares. I also have two black mares, but they are also carrying red factor, so wouldn't necessarily give me black foals, unless put to a homozygous black (EE) horse.

One of my bay fillies has tested EEAA - This means that she will have a bay foal every single time, unless put to something like a coloured, spotted, dilute or grey stallion.
 
Anastasia, definatly worth getting her tested for chestnut as its so cheap and simple, as chestnut can hide for generations and then pop out.

ashbank - I think i prefer my simple version, gives me the same answer without any of the complicated stuff - I kinew being simple would come in handy one day
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I kinew being simple would come in handy one day
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Simplicity is magic. However, when it comes to trying to get specific colours, it's not always the best policy! It's good to know what you're dealing with, and always best to think of things in the correct terms - else I find something will always catch you out.

I've been trying to eradicate red from my breeding programme in favour of black, and then I do the foolish thing of getting a cremello. Thankfully she is homozygous Agouti, so can't throw a black. The people who tested her were so surprised when I was pleased she couldn't have black foals - they said normally people want the recessive homozygote!
 
Gosh - fascinating thread - I'm learning a lot!
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But what's wrong with chestnut? I mean, why would one want to avoid breeding chestnuts? Is there a prejudice against them among WB breeders or something? (I know some TB people don't like them.)
 
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But what's wrong with chestnut? I mean, why would one want to avoid breeding chestnuts?

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Honestly, you try selling a chestnut Trakehner mare!
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Chestnuts are lovely, but I like to be able to calculate what I am going to get on each occasion - call me a control freak - and I like to know when we're getting a chestnut, not have one sneak in unexpected!
 
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That's where we are different, I love the surprise element, even if I have a good idea of what we are going to get.

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I'm not a complete control freak, honest! I only have one which I know 100% what it will be, the others are all down to a 50% chance apart from the Sixtus/Utah which could be black, bay or chestnut - with a 50% chance of patches on top of that. Thankfully I have a selection of people who have already expressed a serious interest, and they all want different colours/genders.
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If that comes out as a coloured filly you should keep it and sell the mare. Should be a nice combination that will really jump!

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If it's a coloured filly, it will be staying well and truely put. I've got potential buyers for it if it is a coloured colt or solid coloured of either gender, so we're covered on all bases! I'll be keeping mum though - she may be a silly filly, but I'm a sucker for a black Trakehner!
 
Re chestnut mares, there may well be some scientific evidence to back the long established aversion on the grounds of temperament.

I won't bore you with the whole theory but it goes along the lines of an individual of a wild species which looses the Agouti colouring (mainly black hairs but have a narrow band of yellow near the tip) in favour of black have been observed to have altered temperaments.

“ It seems likely that there is an association between an animal’s behaviour and the amount of phaeomelanin (Agouti colouring) in its fur” This may be because both coat colour and temperament are controlled by distinct genes which are very close together on the chromosome…. or via a pleiotropism where a gene has more than one, apparently independent effect on the organism”
 
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Black is dominant not recessive

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Would you like to write to Jeanette Gower and tell her that because I'm sure she really needs correcting on that fact

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Just recieved a reply from Jeanette Gower on this subject as follows.

As I suspected, in saying this you are confusing your phenotype with your genotype, wasn't absolutely sure so before I commented I consulted with someone who does know.

"The facts are the colour Black ( ie the outward appearance of the horse - phenotype) is recessive to every colour except Chestnut.
If referring to genes, (i.e. genotype) there are two sets involved. One is the E series which refers to the hair pigment granules, black pigment E which is dominant over red pigment e. In that sense black is dominant, but then we add the action (called epistatic action - not dominant) of the second series, agouti, which refers to the wild colour. A = bay (brown is sometimes included here) and a = black. Here agouti action necessitates black is recessive. "

Personally I applaud her for writing such an excellent fully illustrated book in the first place for this is most definately not the first time she has been shot at and nor will it be the last. Without her generosity in sharing her knowledge and experieance we would all be left falling asleep to the likes of Guerts.

For those who have not read the book I would thoroughly recommend it my copy is the most dog eared in my collection through constant reference.
 
What exactly is the book again? Will certainly have a look for it. Does she cover coloureds and appys or just straight colours ie black/bay/chestnut and things like the dun factor and dilution genes (palominos etc)

I love colour genetics, I guess some people are just freaky like that!

Oh and re: chestnut thing - not sure I beleive it totally about chestnut mares, not when i own the most laid back chestnut mare... mare... horse - that you could meet! I swear she's nearly human!
 
OK I am being thick. So are we saying agouti is actually a colour (pigment) not something that alters the black pigment ???
I still dont understand why thinking of black and red as the only two colours (pigments) and everything else as a gene that affects that basic pigment - be that agouti, tobiano etc etc is wrong. Is agouti a colour in its own right or not?
God I'm confused
 
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OK I am being thick.

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Not exactly.. The genes at the Extension locus are responsible for Eumelanin production. This is the gene which determines whether there is black hair or not. The Agouti genes determine the distribution of black hair. There is an epistatic relationship between the two genes - E can suppress A in effect, as the A/a phenotype is only expressed in horses with eumelanin production "turned on" by the presence of a dominant gene at the extension locus.
 
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a friend of mine has just brought a colt that is said to be tested to be homozygous,he is a black colt .

could this be true or does the horse have to be coloured as well as both his parents.
i have tried looking online but can't find anything

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Can you remember there was an advert a couple of months ago where they were pushing the fact that a particular colt some people were selling was "heteroygous" for colour and would produce coloured foals - and it was noticed and discussed and we thought there was a bit of misleading with science going on?

As in heterozygous isn't 100% colour producer, its homozygous for colour that is the 100%, but those less well informed might have bought him as a colour producing stallion as the way the ad was worded, they seemed to be waving the term around to distract as they are pretty alike.

Not trying to make your friends sound like numpties, but have they heard "homozygous" and assumed homozygous colored and he'll throw 100% coloureds when in fact he's homozygous black and therefore won't unless the mare is coloured?

I'm assuming - and am happy to be corrected - that a colt homozygous for colour would actually BE coloured?
 
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I'm assuming - and am happy to be corrected - that a colt homozygous for colour would actually BE coloured?

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Yes, every time, and must have come from two coloured parents. However, a very minimally marked tobiano can sometimes be registered/appear to be solid coloured.
 
I think Jeanette's book is out of print in the UK but you can get it direct from her website, Horse Colour Explained, there are some extracts as well for taster. It covers all the dilutes, dun pseudo albino, single dilutes, rarer dilutes, roan and broken coats, white markings etc.

http://chalani.net/hce.php
 
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