If you have ever colour-tested a Connemara and got a result such as A/A, A/a or a/a, the letters can look more complicated than they really are.
At its simplest, the agouti gene helps decide whether a pony with black pigment is bay or black.
That matters because it can tell breeders whether a pony can produce black, whether two bays could produce a black foal, and what might be sitting underneath colours such as buckskin, palomino, grey or roan.
What is the agouti gene?
Agouti is the common name for the ASIP gene.
Its job is to control where black pigment appears.
If a pony has the dominant A allele, the black pigment is mainly pushed to the mane, tail and lower legs. That gives a bay base colour.
If the pony is a/a, the black pigment is not restricted in the same way, so the pony can have a black base.
That is the basic difference between bay and black at the agouti gene.
What does A/A mean?
An A/A pony has inherited A from both parents.
If it can produce black pigment, that pigment will be restricted to the points, giving a bay rather than black base.
For breeding, A/A is useful to know because that pony can only pass A to its foals.
It cannot pass a.
So an A/A pony cannot contribute the recessive agouti allele needed for an a/a black-based foal.
A good way to remember it is:
A/A always passes A.
What does A/a mean?
An A/a pony has one A and one a.
If it can produce black pigment, it will normally be bay because A is dominant.
But it still carries a.
That means each foal has roughly a 50% chance of receiving A and a 50% chance of receiving a from that parent.
This is why a bay Connemara can still produce black.
It may look bay, but genetically it can still be carrying the recessive a allele.
What does a/a mean?
An a/a pony has inherited a from both parents.
If it is able to produce black pigment, that pigment is not restricted to the points, so the pony has a black base colour.
An a/a pony can only pass a to its foals.
So:
a/a always passes a.
Agouti does not work on its own
There is one other gene breeders need to understand alongside agouti.
It is usually called Extension or Red Factor.
This gene controls whether the pony can produce black pigment in the first place.
A pony with at least one E allele can make black pigment.
A pony with two recessive red alleles has a chestnut base and does not show black pigment in its coat.
So the simplest way to remember the two genes is:
Extension decides whether black pigment can be made.
Agouti decides where that black pigment appears.
In practice:
E plus A gives a bay base.
E plus a/a gives a black base.
A pony with two recessive red alleles has a chestnut base.
Can a chestnut Connemara still carry agouti?
Yes.
A chestnut pony can be A/A, A/a or a/a.
You simply cannot see the effect of agouti because there is no black coat pigment for it to move around.
That hidden agouti result can still be passed to the pony’s foals.
This is where DNA testing becomes useful, because looking at the pony tells you nothing about which agouti alleles it carries.
Why agouti matters in a palomino
A palomino has a chestnut base with one copy of the cream gene.
Because the underlying base is chestnut, you cannot see the pony’s agouti result.
Two palomino Connemaras could look very similar but have completely different agouti genetics.
One could be A/A.
Another could be a/a.
Both are still palomino, but they can pass very different colour genes to their foals.
That is why agouti can still matter even when you cannot see its effect in the pony itself.
Why agouti matters in buckskin Connemaras
This is probably one of the most useful places to understand agouti.
A buckskin is a bay base with one cream allele.
A smoky black is a black base with one cream allele.
So the difference starts with the base colour underneath.
Bay plus cream gives buckskin.
Black plus cream gives smoky black.
That means knowing a pony carries cream is only part of the picture.
If you are breeding for colour, the agouti result can help tell you what that cream gene is acting on.
Can two bay Connemaras produce a black foal?
Yes.
If both parents are A/a, they can each pass a.
A foal that inherits a from both parents will be a/a.
If that foal also inherits the ability to make black pigment, it can be black.
The possible agouti results from an A/a to A/a mating are:
A/A — around 25%
A/a — around 50%
a/a — around 25%
That does not mean every bay-to-bay mating has a 25% chance of producing black.
If one of the parents is A/A, for example, it cannot pass a, so an a/a foal is not possible from that mating.
The actual DNA results matter.
Can a bay and a black Connemara produce black?
Yes, depending on the bay parent.
A black-based pony is a/a, so it always passes a.
If the bay parent is A/A, it can only pass A, so the foal cannot be a/a.
If the bay parent is A/a, it can pass a.
If the foal gets a from both parents, it will be a/a.
Again, the foal still needs to inherit the ability to make black pigment.
Can two black Connemaras produce a bay foal?
Not through agouti.
Two black-based a/a parents only have a to pass.
So their foals will also be a/a at the agouti gene.
They cannot produce an A allele.
That does not mean every foal must necessarily look black, because other colour genes are still involved.
If both parents carry recessive chestnut, for example, they could produce a chestnut-based foal.
What about grey Connemaras?
Grey can make colour genetics look much more complicated than it really is.
A grey Connemara still has an underlying base colour.
It may be bay, black, chestnut, buckskin or another colour underneath the grey.
The grey gene gradually causes the coat to lose pigment as the pony gets older, but it does not erase the underlying colour genetics.
Those genes can still be passed to the pony’s offspring.
That is why an older grey stallion or mare may tell you very little about the colours they can produce just by looking at them.
What about roan Connemaras?
Roan also sits over another base colour.
A roan pony might be black underneath, bay underneath or chestnut underneath.
That gives colours such as blue roan, bay roan and chestnut or strawberry roan.
Agouti still matters because it helps decide whether that underlying black-pigmented base is bay or black.
It is also worth remembering that not every pony that looks roan necessarily has the same genetic form of roan.
Appearance alone does not always tell the full story.
And what about “dun” Connemaras?
This is where traditional Connemara terminology and modern colour genetics can get muddled.
Golden Connemaras with dark points have long been called dun, especially in Ireland and the UK.
The British Connemara Pony Society still uses the wording “dun (may also be known as buckskin)” in its breed standard.
Genetically, though, buckskin and true dun are different.
A buckskin is a bay pony with one copy of the cream gene.
True dun is caused by a different genetic system altogether.
The true dun allele lightens the body while usually leaving the mane, tail and lower legs darker. It can also produce primitive markings such as a dorsal stripe and leg barring.
There are also non-dun variants called nd1 and nd2.
The important one here is nd1, because ponies carrying nd1 can still show primitive markings, including a dorsal stripe, without being genetically true dun.
So a dorsal stripe on its own does not prove that a Connemara is dun.
Published genetic work involving Connemara ponies has found non-dun genotypes rather than the true dun allele in the ponies tested.
That supports the long-held view that the traditional golden “dun” Connemara is generally what we would now call buckskin.
However, those studies do not represent every purebred Connemara in the world.
For that reason, it would be too strong to say that true dun is absolutely impossible in the breed.
A safer and more accurate way to put it is:
A Connemara described as dun is usually referring to buckskin in modern genetic terms, unless DNA testing proves otherwise.
Does agouti affect health?
No.
Agouti is a coat-colour gene.
A/A, A/a and a/a are not health results.
There is no good agouti result and no bad one.
It simply tells you something about the colour genetics a pony carries and what it may pass to its foals.
That is very different from a health test such as HWSD.
Should Connemara breeders test for agouti?
Not every breeder needs to.
If colour has no bearing on a mating decision, the result may not change anything.
It becomes more useful when you are trying to understand or predict:
black
bay
buckskin
smoky black
palomino breeding lines
hidden base colours under grey
unexpected foal colours
It is also useful if you want to know whether a bay pony actually carries a and therefore has the potential to help produce black.
Colour should still remain only one part of a breeding decision.
Agouti can tell you about coat colour.
It cannot tell you anything about temperament, conformation, soundness, performance or whether the pony is a good breeding animal.
The bit worth remembering
If you forget everything else, remember this:
A/A always passes A.
A/a can pass A or a.
a/a always passes a.
And:
Agouti only shows its effect when black pigment is present.
Once you understand those four points, the rest becomes much easier.
Frequently Asked Questions About the Agouti Gene in Connemara Ponies
What does A/A mean in a Connemara pony?
A/A means the pony has two A alleles. If it can make black pigment, it will have a bay rather than black base. It will pass A to every foal.
What does A/a mean?
A/a means the pony has one A and one a. If black pigment is present, it will normally be bay, but it can still pass a to its foals.
What does a/a mean?
An a/a pony has two recessive agouti alleles. If it can make black pigment, it will have a black base. It passes a to every foal.
Can two bay Connemaras produce a black foal?
Yes. If both bay parents carry a, they can both pass it to the same foal. If that foal also inherits the ability to make black pigment, it can be black.
Can two black Connemaras produce a bay foal?
Not through agouti. Two a/a parents have no A allele to pass.
Can a chestnut Connemara carry agouti?
Yes. A chestnut pony can be A/A, A/a or a/a. The effect is simply hidden because chestnut does not show black pigment in the coat.
Does agouti matter in a palomino?
Yes, particularly for breeding. A palomino is chestnut-based, so agouti is hidden in the pony’s own coat but can still be passed to its offspring.
What does agouti have to do with buckskin?
Buckskin is one cream allele acting on a bay base. Smoky black is one cream allele acting on a black base. Agouti helps determine whether that underlying base is bay or black.
Are dun Connemaras really buckskin?
Usually, yes in modern genetic terms. The traditional Connemara use of the word “dun” generally refers to what genetics now describes as buckskin. True dun is caused by a different gene.
Does a dorsal stripe mean a Connemara is true dun?
No. The non-dun nd1 variant can also produce primitive markings, including a dorsal stripe. DNA testing is needed if you want to know whether the true dun allele is present.
Can a grey Connemara carry black or bay underneath?
Yes. Grey acts over another base colour. A grey pony can still carry and pass the genes for bay, black, chestnut or other colours underneath.
Is agouti testing a health test?
No. It is purely a coat-colour genetics test.