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I saw an advertisement saying:
"This bay, homozygous BLACK, Straight Egyptian Arabian stallion was foaled ....."
So the stallion is bay. Also on the picture he looked bay. As bay is not black, how can a bay stallion be advertised as being black, and homozygous at that??? Black in capitals, too! if the advertisers means to say that the stallion is EE, he can still also be AA and never in his life produce a black foal. Furthermore, it also depends on the mare's colour, what the foal will be. If the advertiser suggests that this stallion produces black, I have my doubts about his colour inheritance knowledge. Or worse....
Or do I completely misunderstand this? Can someone explain?
I'm glad to see someone else bring this up. It can be confusing to a lot of people who don't know the "lingo" of color genetics. But you are completely right. I think a better use of the term would be "homozygous black FACTOR" meaning the horse cannot sire a chestnut foal. I always advise everyone to test for Agouti when testing for black and I believe UC Davis does do them both at the same time as a rule.

If a horse is EE and Aa they "can" sire black as long as the mare is not AA but as you point out, if one parent is AA, even though they are also EE / homozygous black factor, they will never sire black. Everyone should test both potential parents for Agouti before attempting to breed for black. wink.gif
Cat Hill
Exactly, homozygous for black does not imply the horse has to be black. It only means they cannot produce red. They have 2 genes for black so the foal will get one of those black genes regardless the color of the mate so the foal cannot be red. My mare is homozygous blak and homozygous agouti so she can never produce red or black, only bay. Topping that off, one of her agouti genes is bay and one is seal brown (that is what is called black bay in the Arabians). So she can produce bay and black bay only. At this time, she's had 3 foals and all 3 were black bay but she is a true bay.

If a horse is black itself, and is homozygous black, it can produce black but not bay unless bred to bay and cannot produce red (chestnut). There is no need to test for agouti status with a black horse, they are always aa. A red horse (chestnut) can hide the agouti though so a chestnut can have AA for the agouti (homozygous) and never be able to produce black so they should be tested if you wanted to breed for black because all you'll get is chestnut and bays. A bay should be tested unless they have produced a black. If a bay can produce a black, then you can be sure they are Aa. Knowing the color of the foals a mare or stallion has produced can give you a lot of information about their color genes without testing.

I hope I'm not muddling it more for you.
No worry, I understand you perfectly. I do understand the inheritance of the basic horse colours. It is the advert I do not understand- I have the feeling that the owner tries to suggest that the stallion gives black offspring, which is not supported by the information of homozygous black, if that means EE. By the way, also a bay horse needs not be tested, when it is the result of a chstnut and a black parent: it can only be Aa Ee. Also a bay offspring of a (tested) aa ee chestnut can only be Aa Ee rolleyes.gif
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