Disclaimer: If you have a specific hobbyist/club sort of focus on color breeding, the discussion below might be of limited value to you or could be wrong or incomplete from the perspective of your hobbyist organization. Hobbyist organizations will have specific terms for things that could be different from what I have written here (there may even be differences between organizations). They could be making distinctions within genotypes or phenotypes that I'm not writing about. Your organization may be making color-specific, important (to you) "qualitative" (air quotes, sorry) determinations. These things have no scope in my own breeding focus, so in terms of what I write, you get what you get, if you choose to read it.

• AA BB CC EE PP SS rnrn

• replace all Dark with Red's color except for the eyes;
• lighten Dark from its default black to brown (+ reddish eyes)
  
• transform all Red to white color
  
• lighten Dark to be lilac (+ red eyes), and lighten Red to be gold

    When guinea pigs are called "Self", this is supposed to signify:

• it's not agouti (aa),
• the Dark and Red have not been split into patches by the extension gene (e^p),
• it doesn't have white spotting (SS)

    A = Agouti.

Agouti is the wild-type fur patterning where each hair has more than one color on it. The base of the hair is "Dark", the tip of the hair is "Red", except for the fur on the underside of the body, where the hairs are solid "Red". Possible mutations are (ar), (at), and (a).

If the guinea pig has two agouti genes with the (ar) mutation, it makes the fur on the underside stop being solid "Red". The multicolor hairs are there too. This is known as "Ticked belly" or "Solid" agouti.

Two agouti genes with (at) mutation makes for extra multicolor hairs being replaced with solid "Red" ones in certain places, such as around the eyes, chest, and other highlight-looking areas. This gene is the backbone of what they call Fox, Tan, Marten, and Otter guinea pigs (not sure if more names). The exact names are determined by what their other color mutations are (especially the mutations on (C) ).

If one gene is (ar) and the other one is (at), the effects of (at) do not happen (ar is dominant over at). There isn't anything in the symbol system itself to help you know that, at least as the online Cavy Calculator is doing it (in theory you could say that (ar) is more like (Ar) ).

Two genes with the (a) mutation makes the agouti patterning disappear. The "Red" will not display unless a different mutation drags it back out again (such as e^p or e^e).

(ar) and (at), if one of them occurs with (a), are both dominant over (a) and will override the agouti-disappearing-act.

Caveat: agouti fur patterning disappears from the phenotype if both E genes show up as mutated ee.

Red agouti teddy baby with a sweet little white face

    B = Chocolate.

The letter B was meant to mean "Black eyes". When non-mutated, it is represented as capital B and you could have a black guinea pig (with dark eyes) from that. But in application, it's the Chocolate gene (as you think of its mutation).

In isolation: When this gene is mutated as lowercase b, and the guinea pig gets this mutation from both of the parents (bb), it makes a "chocolate" guinea pig. It turns guinea pigs "Dark" color into chocolate brown and the eyes turn a little red.

The eyes are slightly glowy-red on chocolates.
If a pp gene is loaded up too, the eyes are much more glowy-red.

In the real world: The "Dark" can additionally be affected by other genes, all stacking their effects on top of whatever bb might have caused.

Caveat: There is a gene characteristic called dapple. It is not well-known worldwide. At least one group of guinea pig enthusiasts gave this trait the letters "wd" (white dapple).  Dapple will cause some individual hairs on the "dark"-colored areas of chocolate guinea pigs to be white, as long as the guinea pig has at least one C gene (capital C). I wonder if the wd gene is actually a version of chocolate. If that's true, it would be like b^wd or something.

Here's some tri-color chocolate teddies I had pop out with dapple on them.
Notice how the red-patched areas look normal. The one on the bottom had both chocolate and another "Dark"-affecting gene in effect (something on both (P) genes I guess).

C = Albino (but not really). "The white gene" "cream" "it's complicated"

When C is not mutated, it endeavors to display the "Red" at full intensity, and largely doesn't do anything to the "Dark".

There are a pile of mutations available on C. Some of the mutations are like (c^r), (c^d), (c^a) as is shown in the online Cavy Calculator, but there could be more. When different mutations are received from parents, they can mix up and make variable effects. I wonder if the difference between the C-mutations are actually DNA-repeats.

• C's mutations (when received from both parents) lighten "Red", and instead you get buff, cream, maybe everything in between red and white, and a transformation of "Red" to pure white is possible.
  

• Pink-eyed whites! (PEW). One of these C-mutations (c^a), when received from both parents, creates an albino-appearing guinea pig with pure white color and pink eyes. Except that it's not a true albino. Real albino animals have color that is so non-functional that absolutely no color can ever be made. Areas of PEW's skin that are exposed to cool temperatures can have "dark" start appearing in those places.

• A double-hit of C-mutations that aren't both PEW mostly don't affect the "Dark" color, but it makes for a shift in the "Dark" toward Sepia and Sable. Those colors are more like a charcoal black instead of the regular black.
  

• C-mutations are part of how you create dark-eyed whites:

• First, when there's 2 mutated E genes (ee), it makes all of the "Dark" be transformed into "Red"
  
• Then, when there's 2 mutated C genes (ideally 2 copies of c^r), it takes what it sees as "Red", and dumps it to white.
  

Poof, white guinea pig! And the eyes are not brilliant pink. Like the PEW, dark hairs will appear in response to exposure to cool air.

• You get exactly the same appearance using (c^r) + (c^a) but those will pass a PEW gene to half of their babies, which is maybe not perfect if you want to breed from them.
  

I've had a lot of c-mutation guinea pigs. Cream, buff, pale, white -- like a red-to-white rainbow.

1 litter with 3 red-derived colors

Blizzard had an open window near him for a bit

E = Extension.

Extension has 2 mutations. They are pretty powerful mutations, as mutations go.

One mutation conveniently breaks the "Dark" and "Red" into separate patched areas on the coat (e^p).

Notably, if the guinea pig has both a non-mutated E gene plus this mutant (e^p), the mutant can mess with the phenotype a little and make a small patch of red. Mutated genes usually cannot do things like this -- they cannot mess with the phenotype if a non-mutant is also present. They call this situation "incomplete dominance", but it could have been more interesting to call it "Super Mutant".

Extension has another mutation (e) that will, if two are inherited (ee), rewrite all the "Dark" areas on the guinea pig with "Red". So, the whole thing is some version of red. When it does this, if agouti was supposed to be there, it gets deleted from the phenotype (and yeah, it still passes agouti genetics to babies). Like I was saying, we got Super Mutants in this gene.

Plus, the (e+e) mutation is the first step in making the two-step dark-eyed white.

Wilbur was a Super Mutant (E and e^p).
See the small red patch above his eye?

If a guinea pig gets one (e^p) and one (e), the e^p mutation is dominant over e. But having said that, this is a super mutant sort of gene. I can't personally say for sure if the combo (e^p + e^p) has a phenotype difference from (e^p and e), but the online Cavy Calculator says it doesn't.

A "brindle" pattern is when e^p happens to make a sort-of fuzzy-edged striping or splotchy pattern, maybe with the red/dark hairs intermixed, instead of solid-edged squares or similar. The gene modifiers that make for brindle are not documented in the symbol system as far as I can see, so this term might be arbitrary.

This young boy was getting that brindle pattern going

Magpie. Could be more of an appearance observation than a genetic type, the genetic core is like this:

• at least one of its extension genes is (e^p) and the other gene, if not also (e^p), is (e).
• at least one of its C-genes is the dark-eyed white (c^r) and the other one, if not also (c^r), is the PEW gene (c^a)
  

So: e^p creates a patching pattern. And, the specific mutations on C transform the red patches to white through one of the combinations that does not, also, eradicate the "Dark" color completely (ie: never two PEW genes (c^a + c^a)).

This makes for areas of black (or chocolate or sable), + separate white areas, dark eyes, and absolutely no red patching anywhere. Some Magpie enthusiasts seem to be looking for a coat pattern with bi-lateral squares but a lot of what I'm seeing around is a brindle pattern.

I think Magpie can be a little tricky sometimes.

-- It's theoretically possible for a genetic Magpie to be a phenotype, essentially fake, dark-eyed white. If the would-have-been black area happens to be small, and the white spotting gene is hitting hard and makes a white patch that covers that completely, there you go. I've seen one that came very close, all white with dark eyes but one small black patch was showing.

-- There is another black and white phenotype, an E-looking guinea pig with a heavy hitting white spotting gene. From what I've seen, the white spotting gene will tend to form blobs with cleaner edges, it's not like the brindle pattern I keep seeing on Magpie (+ Harlequin). But the thing is, if you get a mostly-dark Magpie with a big hit of the white spotting gene, maybe the white spotting covers up what would have been a brindle part of the dark area.

-- As a third possibility,  on an otherwise mostly-black guinea pig, some small amount of red patching caused by e^p could be completely covered up by the white patching gene. ...

I think with black-and-whites its helpful to know something about the parents or see the littermates because otherwise it can get a little weird when the babies start showing up.


Harlequin. The Cavy Calculator doesn't mention Harlequin - I think it's not exactly a genotype, moreso an appearance. The genetic core is like this:

• Extension mutation creating a pattern: at least one of its extension genes is (e^p) and the other gene, if not also (e^p), is (e). I think they might expect the patching pattern to be brindle, but some of the pictures have a blocky pattern that is fuzzy around the edges. I'm not the right one to tell you if some specific pattern is more "correct" (air quotes) for harlequin.
  

• C-gene ... mutate to "cream" or "deep cream" or "yellow", apparently?

• I'm seeing enthusiast pictures which include a range from the very lightest cream approaching buff. The "cream" determination may be a bit arbitrary.
  
  What they seem to be asking for in C requires one buff mutation (c^d), and the other one would be one of the white genes (c^r / c^a). They might prefer one combination over the other, I couldn't tell you that part.
  

• They are asking for black color in the "Dark":
  
• requires (B) (not chocolate bb),
• requires (P) (not lighter slate/lilac from pp),
• not anything else that lightens "Dark" (whatever it may be)

•  (S) They apparently don't want white spotting on these.

This baby was Harlequin genotype,
and popped out with that brindle pattern going hard
(no squares, though. Very stripey!)

P = Lilac and Slate.

The letter "P" is supposed to mean "Pink eye". But there are other genes which also make what we would call pink eyes.

I have not focused on this mutation in my breeding (although one of my boars carries it, and made some very funky babies with a few of my sows). But anyway, here's what I'm seeing about this:

When both of the P genes are mutant, and one of them is (p^r), black (B) becomes slate and chocolate (pp) becomes "coffee", and there will be some pink/red effect in the eyes.

When mutated as (p+p), it lightens "Dark" even more. Black (B) becomes "lilac", chocolate (pp) becomes "beige" + pink/red effect in the eyes.

Two hits of mutated (P) also affects the "Red". I feel like the names they gave these colors may be a bit arbitrary, with some enthusiasts not being consistent between one another. But for some of them, anyway: red (C) is being called "gold", buff (c^d + c^d) is being called "saffron", cream colors hit with this are being called "lemon".

The eyes don't look exactly like the pink-eyed white eyes, at least not the ones I had. The PEW eyes were kind-of more pale-pink than these.

It looks like "Argente" is what they call an agouti that has a double hit of mutations on this gene, but this word clearly has some arbitrary character to it, since I can see that some enthusiasts were picking / choosing / making changes / as to which p-mutations they wanted to call Argente.

This is a teddy with a double-hit mutation on (P).
Nadja says it looks like a "lilac" one (I don't know much about these).

S = White Spotting

This is a weird mutation that affects the fetus as it is growing in the womb. Also, it is another Super Mutant. If one mutant gene is present and one non-mutant, there will be some effects on the phenotype.

There are color cells that migrate across the skin as the fetus is forming. With this white spotting mutation, this process is messed with. There's whole patches of skin that the color doesn't happen in and those areas come out white.

Almost everything I make has this mutation. I noticed that the white patches often avoid the eyes and ears. It likes to make a circular area around the neck and shoulders and a white blaze of variable size on the head (sometimes this extending to cover some part of the face). It can make large white patches, or a big stripe somewhere, or random white markings.

I think a lot of show breeders do not like this gene (except for the ones who are trying to make "tortoiseshell and white" or straight-up black and white). Their loss! It's great when making pets for real-world pet owners.

The baby in the middle has a white stripe.

Rn = Roan.

Roan is a little backwards.

For one thing, the mutation is dominant. One mutated gene of (Rn) combined with the un-mutated (rn) should give you a guinea pig with that "roan" appearance (which is some amount of widely-scattered white hairs, which if there are a lot of them, are less-present on the head).

And then, if the guinea pig inherits the mutation from both of its parents (Rn Rn), it is born all screwed up and mutated, as a "Lethal White".

A "dalmatian" gene would be, a version of the roan mutation which makes for a somewhat distinct pattern of black spots. Like roans, 2 genes of dalmatian inherited by the same guinea pig make it be a screwed-up, mutated "lethal". Same goes for 2-gene dalmatian + roan.

I got no pictures of roans or lethal whites or dalmatians to show you, but you could look around the internet and find some.

It's reportedly possible to have a guinea pig with the roan/dalmatian mutation and not realize it because it's not meaningfully displaying in the phenotype. Then, there can be a nasty surprise when a lethal baby pops seemingly out of nowhere, as 2 roans have been accidentally bred together. Reportedly, a single white hair can mean that roan is hiding out in the genotype. But nothing like this has ever happened to me.

I think someone would have to be crazy to intentionally breed 2 of these together while understanding how the whole lethals thing works.

---

These aren't the only color combinations, and there are additional mutation forms of these genes being documented (at least on the internet). In any case, they are well-known ones.