Agouti question: "black" and "homozygous for black points" -- impossible, right?

[columbus]

This is the most confusing color post I have ever read. I was so confused I had to reexplain it to myself.

Usually, a stallion is advertised as ‘homozygous black’, He would be EE. If his color is black he is aa too. All offspring will be E_…no chestnuts(e) possible. So saying homozygous black means no chestnuts foals…it doesn’t mean you will produce blacks…the mares genotype will determine if there can be black or bay, but even if the mare is chestnut (ee) she will never have chestnut foals bred to a homozygous black stallion. A chestnut always is ee. The homozygous black stallion has no e to contribute. Many people…like the Holsteiner Verband dislike chestnuts…this is how you prevent chestnut offspring.

If they said he was a homozygous bay(AA) then you know that even if he looks black he is in fact a dark bay. A means black will be in the bay pattern…a means the balck will be all over…A is dominant over a…so bay pattern is dominant over black all over. All his foals will get A_ and will be some shade of bay. He can also be AA EE (homozygous bay AND homozygous black)but you will not see that expressed all the foals will be bay because A is dominant, because he only passes E none of the foals will be chestnut regardless of the mares phenotype.

Ee says whether there is black to modify…E black…e no black.
Aa says what happens to the black…A bay pattern…a black all over

Now…grey…changes any color to white over time. Grey is also dominant over non-grey. A homozygous grey will make all offspring grey eventually. Their base color is still there but it is modified by the grey gene if it is present. A heterozygous grey will have 50% greying foals and 50% non-greying foals.

I just bought a heterozygous grey stallion. We don’t know his genotype but we can use the evidence of his offspring to determine his genotype.

Laird is grey.
Laird has non-greyed offspring so he is heterozygous for the greying gene…50% chance a foal will be greying.
I don’t know the color Laird was foaled as.
Of the foals Laird has had(~20) none of them are chestnut…none of them are black. However, we have some grey offspring and we don’t know what color they greyed from.
20 is not a very large sample. It could be that like the Holsteiner Verband most of the dams he was bred to are bay or black…or greying.
If there was ONE chestnut offspring we would know Laird is heterzygous for the red gene Ee and can pass either E_ or e_
If there was ONE black we would know he is heterozygous for the bay pattern gene Aa passing either A_ or a_
As it stands with the evidence we have he is for sure Gg A_E_ and evidence to hand says Gg AA EE a black offspring would change the AA to Aa and a chestnut offspring would change the EE to Ee.
PatO

[JB]

I don’t think you can say for sure he’s A? or even E? The chances are good he is, but as you said, 20 kids isn’t enough.

Combine that with having some unknown pre-gray color kids, and not knowing the colors/genetic makeup of the mares he bred, many of whom might well be EEAA themselves, there’s nothing you know for certain now except him being Gg

Chances are pretty darn good that foaling 50 foals in a season would give you roughly 25 colts and 25 fillies, give or take. But Equine Repro not only had 49 colts and 1 filly, but the 49 were all in a row :eek: So, 50 foals isn’t even enough to really say what the deal is LOL

[columbus]

Agreed. Need more evidence…it is a bad guess…and only a guess. So FAR only bays and greys is all we can say…oh so…we know he IS heterozygous grey. PatO

[Tapperjockey]

[QUOTE=columbus;6151189]
Agreed. Need more evidence…it is a bad guess…and only a guess. So FAR only bays and greys is all we can say…oh so…we know he IS heterozygous grey. PatO[/QUOTE]

Thank god that they have tests now haha.

[L_L]

[QUOTE=columbus;6151189]
Agreed. Need more evidence…it is a bad guess…and only a guess. So FAR only bays and greys is all we can say…oh so…we know he IS heterozygous grey. PatO[/QUOTE]

A horses parentage can also help you determine certain peices of his genetic makeup even before any offspring are born.

If either one of his parents are non grey then you are 100% certain he is hetrozygous grey.

If either one of his parents were chestnut or born chestnut then greyed out he will carry red.

You also need to know what colour his foals were born to conclusively say he has sired no chestnuts and no blacks. He may well have sired chestnuts and blacks that have simply greyed out as adults.

If he has sired bay progeny the dam could have passed on her agouti to make the foal bay, he could still be agouti negative (black)

Are his bay progeny mature adults with no signs of greying out Columbus?

Simple solution pull a few hairs and test

[Fillabeana]

Really? Ive never heard that, tapperjockey, but I’m no expert so you are probably right. I know that what I said is correct for buckskins, but I was thinking that every horse has the agouti gene and that when it is dominant the horse will have black points and when it is homozygous recessive the horse will not. I was thinking that maybe it just did not show up on black horses because they are, well, black

Skippy, you seem a bit confused.
Not every horse has the agouti gene. Otherwise you would never have true black horses, only really blackish seal browns.

Every horse does, however, have TWO GENES AT THE AGOUTI LOCUS.

Locus means location.
If we pretend that the DNA, simplified, is like a double stranded plastic-pearls necklace, that has 60 beads on each strand. Now imagine that each plastic pearl has a number on it. And also imagine that the two strands are attached to each other, each numbered ‘pearl’ is attached to its same-number plastic pearl on the second strand.

-O-O-O-O-O-O-O-O-O-O-O
-O-O-O-O-O-O-O-O-O-O-O

Picture a tiny little number on each O, and imagine that they are connected.

Now, since we can run a genetic test, we (well, the genetecists anyway) know precisely which “numbered plastic pearl” [LOCUS] (say, for fun, number 13) would have the Agouti gene. So we can ‘look at the necklace’ in a genetic test, at the two “13” pearls [agouti locus], and see if they have “Agouti” ‘written’ on them.
If a horse is bay, (base coat, this would include buckskin and dun and some grays, among other modifiers), at least one ‘number 13’ pearl has Agouti ‘written’ on it, and perhaps both pearls do.
If a horse is black, neither ‘number 13’ pearl says Agouti on it.
That ‘number 13 pearl’ is simply a visualization of a locus (location) on a strand of DNA. So of course every horse has two genes at the Agouti location. But not every horse has the Agouti gene.

[Reed_Hill_Farm]

ANIMAL GENETICS INC. in Tallahassee, FL

http://www.horsetesting.com/Equine.asp

is a super fast place to get your horses hair DNA’d to check color/pattern.

red/black/agouti test is only $40.

Good Luck!

[STF]

Actually, “dark points” IS how UC Davis words the EEAa and EEAA color codes, which means that is not uniformly distributed black color pattern meaning (dark points).
This is an actual recent test that was recently done from my young Trakehner colt… and the exact wording used with the 2nd page of color explanations.

http://www.spindletopfarm.com/UCDavisColorTest.pdf

And here would be your color chart % rates depending on the mare bred -
http://www.vgl.ucdavis.edu/services/coatcolortable.php

So I think that is where the person is getting Homoz for dark points from.

[JB]

Ee would still fit that category too Assuming A? of course

[vtdobes]

@columbus;6151069

He can also be AA EE (homozygous bay AND homozygous black)

I think this is where people get confused. A horse cannot be both a homozygous black AND a homozygous bay. If a horse is EE AA he is a homozygous BAY (he is homozygous FOR black BASE which includes black, bay, brown but he himself is NOT homozygous black).

[JB]

yes, if a horse is EE, regardless of what color he is (perlino, buckskin, brown, bay, smoky brown, grulla, etc ) he IS homozygous black.

He just may not be black.

EEAACrCrDD is what RFF Starbuck is. Perlino and dun. He’s homozygous black, homozygous Agouti, homozgyous cream, and homozygous dun.

[vtdobes]

@JB;6276235

yes, if a horse is EE, regardless of what color he is (perlino, buckskin, brown, bay, smoky brown, grulla, etc ) he IS homozygous black.

He just may not be black.

And that’s why people are still confused. He is not black…he is homozygous for black base.

[JoZ]

Wow how did I lose this thread – and it’s mine! Lots of good info and I’m following it which is a good thing.

Columbus said:
“If they said he was a homozygous bay(AA) then you know that even if he looks black he is in fact a dark bay. A means black will be in the bay pattern…a means the balck will be all over…A is dominant over a…so bay pattern is dominant over black all over. All his foals will get A_ and will be some shade of bay.”

I’m assuming s/he was referring to the stallion I was asking about (who indeed is Rosenthal), not a hypothetical case. But just to be excruciatingly clear – a horse can be chestnut and be homozygous agouti (AA). And even in the case I posted, unless he is also homozygous for black, he can have a chestnut foal if neither he nor the mare passes a black gene. Agouti without any black to work with is invisi-gouti.

Right?

[vtdobes]

[QUOTE=JoZ;6276355]

But just to be excruciatingly clear – a horse can be chestnut and be homozygous agouti (AA). And even in the case I posted, unless he is also homozygous for black, he can have a chestnut foal if neither he nor the mare passes a black gene. Agouti without any black to work with is invisi-gouti.

Right? [/QUOTE]

Yes. The horse can be a chestnut (ee) and also be heterozygous (Aa) or homozygous (AA) for bay (or it can be aa). You can’t tell though by looking at the horse as it has no effect on red hair.

And yes if he is Ee he can have a chestnut foal (unless you breed him to a EE mare).

[JB]

@vtdobes;6276319

And that’s why people are still confused. He is not black…he is homozygous for black base.[/QUOTE]
Yes, some people get confused when someone says a horse is homozygous black and think he has to also be black. That’s not correct. EE/homozygous black only means he can not produce a red-based foal. It in and of itself tells you nothing about what color the horse actually is. He might be black, but he might be any number of other colors - bay, brown, perlino, buckskin, grulla, and more.

However, your comments were not correct, whether you intended to write what you did or just missed a few letters

[QUOTE=vtdobes;6276142]I think this is where people get confused. A horse cannot be both a homozygous black AND a homozygous bay.

Absolutely can - EEAA is both homozygous black (EE) and homozygous bay (AA). The EEAACrCrDD example is also both homozgyous black and homozygous bay

If a horse is EE AA he is a homozygous BAY (he is homozygous FOR black BASE which includes black, bay, brown

In a sense, yes, as in, when bred to any other normal color - black, bay, chestnut, he’ll always produce an E?A? horse, meaning always bay (or brown).

but he himself is NOT homozygous black).

Because he is EE he IS homozgyous black.

[JoZ]

I wish we could add in the word “for” – homozygous FOR black, homozygous FOR agouti, homozygous FOR tobiano. And I’d further stipulate that those should be the only possible terms. No “homozygous bay”, “homozygous black points”, “homozygous paint”.

Don’t know if I’d include “homozygous for cream factor” but maybe. “Double dilute” does seem to be pretty straightforward and commonly known. But I’ve inquired about a homozygous buckskin (that turned out to be homozygous for black) and a homozygous pinto with solid foals all over his progeny page (also turned out to be homozygous for black). There shouldn’t be so many ways of saying the same thing (with varying degrees of clarity/simplicity)! stomps foot

[vtdobes]

[QUOTE=JB;6276473]

Because he is EE he IS homozgyous black.[/QUOTE]

I will agree to disagree. But there is no way I’m calling my EE AtAt mare “homozygous black” when she is in fact “homozygous brown” and can never in her lifetime produce a black foal

[JB]

Any geneticist will say an EE horse is homozgyous black. Homozygous “for” black as JoZ said.

The Extension gene is the red/black gene. If it’s EE, it’s homozgyous black. If it’s ee it’s homozgyous red. If the Agouti is AA the horse is homozgyous Agouti.

It’s just that how you worded things was very, very confusing given how most talk about and interpret this.

[vtdobes]

And that is also what I said…“homozygous FOR black”.