One of the most common sources of confusion is how the different genes interact. We've tried to explain this in various places on this site, but sometimes it just helps to have pictures. Before we start, there are a few basics to cover.
- All genes come in pairs
- Genes can be "dominant" or "recessive." A dominantG gene is always visible, no matter what it is paired with. A recessiveG gene is only visible when the other half of the pair is the same recessive (homozygousG).
- Dominant genes are not always "good" and recessive genes are not always "bad" (nor is the opposite true).
- Merle (M) is dominant to solid (m).
- Black (B) is dominant to red (b), and there is no visual clue to know if a black dog is carrying a red gene (although there is a DNA test that can be done).
- Ticking (T) is dominant to no ticking (t).
- There are several genes for white trim, but to put it most simply, "less white" is dominant to "more white." In other words, a dog can be carrying more genes for white than what you see.
With that, let's look at some possibilities (keep in mind that these are predictions, and will be truest for large numbers - a litter of pups is a small number, and may not exactly reflect these diagrams). We also did not include copper and/or white trim, since they are inherited separately and we didn't want to confuse the issues more.
We'd like you to notice (as you read along), that there is no such thing as a "double merle" gene. "Merle" is a single gene. It can be combined with either another merle gene (creating a Double Merle dog), or a solid gene (creating a normal merle).
Solid X Solid
If both parents are solid, all the pups will be solid too. Just for fun, we've chosen a "red factored" black dog (meaning that he carries one gene for black (the color that shows), and one gene for red (which is hidden), so he is Bb (phenotypicallyG black, but heterozygousG, so he carries genes for both black and red). If we had chosen a dog homozygous for black (BB - no genes for red), all of the pups would be black.
Our solid red dog is bb. This means that the pups can only get a b gene from her. She is homozygous, and both her genotypeG and phenotype are the same. The litter of pups should end up being half and half, and all of the blacks will be red factored.
It is impossible to get a merle pup from this combination. If you do, something isn't right! (Either one of the parents is actually a cryptic merleG, or Mom had an unauthorized visitor.) A DNA test can be done to determine if the merle pup's parents are who you think they are. If so, then one of them must be a merle (unfortunately, at this time, there is no test to determine if a dog is merle or not).
Merle X Solid
In this litter, half the pups will be merle and half will be solid. We're chosen a blue merle dog for the example, but it is true for red merle dogs as well (we aren't adding red to this example, as it confuses the issue). A merle dog carries one merle (M) gene, and one solid (m), and again, each pup will get one or the other.
This dog is solid black (no merle), so she is mm and can only give her pups a solid color gene.
Merle X Merle
This is the litter where the double merle pups show up (and we don't recommend it). We're using red merle for this example, but the color of the merle doesn't matter. Notice that you will still get solid color pups, since each parent still carries a solid gene.
This dog is also a red merle (but could be blue), and can give each pup either a merle (M) or a solid (m) gene.
Double Merles would never be born, by simply not breeding Merle x Merle!
Although these are possible merle combinations, we don't recommend them. We list them here to provide a few other examples, hopefully illustrating more clearly how the genes interact.
The first is a blue merle crossed with a blue Double Merle (again, red would work the same).
This second example is a red Double Merle and a red solid (blue double and black gives the same results). Each pup will get a merle (M) gene from the Double Merle parent (since he has no solid genes), and a solid gene (m) from the solid parent, so all of the pups will be normal merles (Mm).
Occasionally, it is possible to get a solid pup from this combo, but very, very rarely. The merle gene is believed to be "fragile," which means that sometimes it will "break," and a solid pup will show up. It could happen in other crosses too, but since solid pups are already expected, they aren't noteworthy. This is not a common occurence though.
Although they can sometimes resemble each other, ticking is very different from merle (see pictures on our Ticking page). Ticking is still a dominant gene, but "doubling up" on it does not cause any problems. It is a possibility that dogs who are homozygous for ticking will have heavier ticking that those that are heterozygous, so we've used Tt dogs in our example.
Ticking and Merle
This is a frequent question, so we're addressing it here! We decided to use a merle (Mm) dog with no ticking (tt), which is Mmtt, and a solid dog (mm) with one ticking gene (Tt), which is mmTt. The diagram shows all the possible options (ticking will vary more if you add more ticking genes to either dog, however, we don't want to muddy the waters further). The amount of white on the pups will also vary, depending on how much white the parents have (we aren't delving deeply into that either, as it quickly becomes more complicated). As with anything in nature, absolute predictability is impossible.
This dog is colored like an Australian Cattle Dog with no patches. The graphics in this diagram do not accurately reflect the amount of white that the various combinations would have. They are just showing that variety is possible, not that the ticked dogs will necessarily have more white than the merles.
The White Aussie Project 2003-2005