The merle gene is a gene in dogs which can be a bit hard to explain. You know how if you put food dye into a cup, and then add water to it or maybe white paint, it becomes a lighter color? That is basically the merle gene, it dilutes a dog's color or pigment, if you want to be more technical. However, many breeders are wary about the gene because it does carry the possibility of harming the dog, if bred incorrectly. Unfortunately there are also those who feel the gene should not exist in dogs all together, because a few breeders didn't do their research before breeding.
Anyway, the merle gene can affect any color. I have seen others say otherwise, such as red dogs cannot be affected by the merle gene, but that is incorrect. True red dogs (some breeds use "red" instead of "chocolate", but we are talking about recessive red here, not chocolate) can be affected by the merle gene. Only those who are a very light shade of red, will have the merle gene be hardly visible, if at all, but they still carry it and produce merle puppies. This is where "cryptic" or "phantom" comes in, a cryptic or phantom merle is a dog who is merle, but hardly if at all has any visible indicator that it carries the gene, as though the gene is a ghost, hence phantom, and it is hidden, hence, cryptic. Here is a red roan American Cocker Spaniel, whose only real indicator of being merle is her blue eyes. She does have a bit of fading on her rear, but you can hardly see it in photos.
Some like to say that ACS's (American Cocker Spaniel's) who have blue eyes are "extreme piebald", which is a whole 'nother subject, but it is a gene similar to merle, yet at the same time, completely different. Put simply, it is a gene where a black dog is covered with white, leaving only small spots of black. If the dog has no black on its face or ears, it has a high chance of having blue eyes, but it has nothing to do with dilution. Obviously, this dog is not extreme piebald since it has solid color on the face instead of just spots of color, so such a theory is invalid. It is even actually quite abnormal for a merle to ever have blue eyes without the face having any dilution at all, which you can see on this dog that the right of her face has no dilution, but her left has dilution because of the white/cream you see. So it is possible that this dog is not merle, but then, how would you explain her having merle pups? That is the clearest indicator a merle can ever have, is that if they don't or even do look merle, they will always produce a merle, if not multiple merles.
 |
| A picture of the same dog, with one clearly merle puppy. |
Her daughter is also merle, but does not look it. She was clearly merle at birth, but the Shih Tzu fading gene diluted her color, including the merle, so much so, that you can hardly tell she is merle. Her blue eye is the only obvious indicator, but to the more trained eye, she also has silvering on her black tips (black tipped ears are caused by the sable gene).
Here is Romeo, a buff merle American Cocker Spaniel, who also has hardly any visible merling, and both of his parents did not show merle, but he has produced merle pups, once again proving that he is merle and not extreme piebald.
 |
| Romeo's parents, and growing up. |
 |
| One of the puppies produced by Romeo. Has more color than his brother behind him, yet has blue eyes, proving he is not extreme piebald. |
I think this is enough to show and prove that red dogs can, in fact, be merle. It also shows how incredibly easy it is to actually make a cryptic merle, I found it pretty amazing, considering that people always treat cryptics/phantoms as something rare, when actually its not hard to do at all.
Here is a chocolate puppy, who is merle, but a combination of his long fur and the sable gene, made his merling hardly visible as well.
 |
| Impressive, eh? |
This is why I love dog genetics. It is fun to play around with them and see what the different results yield. You unfortunately can't do this with purebreds, as they are restricted in how a dog looks, and such experimentation is forbidden. I am in no way a professional geneticist, I can't look at my dogs and their puppies' DNA, though I wish I could, and would like to in the future. This is merely what I observe and has no solid evidence to back it up.
