Do all Bays carry Black genes??

[Ms. Trouble Maker]

Well she isn't black...but she may turn out to be a mealy bay just like the sire

[Ms. Trouble Maker]

I believe this is a black Friesian I just got!!

[MoonRiver130]

As far as real genetics, yes. I'm assuming it's the same with the game.

[Hazel]

Yeah, bay needs at least one copy of black to show.

[Ms. Trouble Maker]

How is this color explained?? Does there have to be a black copy in order for seal brown to show up?? Or does the Agouti allow more of the body to be black

[Deslumbrar]

Bay and brown are technically both Agouti, its just hypothesized currently that brown is a slight modification of agouti.

For any sort of
agouti to show, there is a copy of black

[nyraeia]

You can think of brown/bay/wild bay as modifications to black.

a means no Agouti.
At means brown.
A means bay.
A+ means wild bay.
I listed these in order of dominance, so A is dominant to a; A+ is the "strongest" of them all.
--> a < At < A < A+ (= black is weaker than brown; brown is weaker than bay and bay is weaker than wild bay)

Every horse has two of these genes, for example a/a; A+/At; A/a and so on.
Only the "stronger" gene of these two will show, so a horse with A/a will always be bay and never be black (as the bay gene is stronger than the black gene)

Since you want to breed black Friesians, and black is the weakest gene here, your horses will have to be a/a. When you breed two horses, the foal will get one gene from each parent, so a foal from a A/At mare will either get A or At from her (it's random). It may be a good idea to breed in completely black horses (a/a). The resulting foals may not be black themselves, but they will have at least one a (because pure black horses cannot have anything else, or they would be bay or brown).
Let's say your foal is At/a (which will look wild bay, remember?). If you have another horse with a black parent, let's say A+/a, which possibilities are there?

First horse can give At or a.
Second horse can give A+ or a.

Possibilities (these are all equally likely):
At/A+
At/a
A+/a
a/a
Only the last one will be a black foal. That's one of four. So about 25% of the foals of two horses that have one a gene each will be black.

On chestnut-based horses, every version of Agouti is invisible. So if you can't say for sure that a chestnut horse has at least one a gene (for example if it had a black parent), you don't know what you're going to get. It may have A+/A and you will never get a black foal out of it.

[Ms. Trouble Maker]

ah ok I think I get it now!! And wow! that's crazy...no wonder I was never getting a black one. But both parents were mealy brown and a sooty mealy brown.

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[nyraeia]

As they produced a black horse but are brown themselves, we can conclude that they must both be At/a. :)

[Ms. Trouble Maker]

wow...that must be sorta rare I'd think...but cool!!