The Dilute Gene - Blue x Blue is okay!
Examples of Dilute in Chihuahuas all the above dogs have been DNA tested as d1 or d3, or both.
We are asked if a blue Chihuahua can be bred to a blue Chihuahua. At first, I was thrown off by this as I had not heard of this being an issue. After reading about Chihuahua groups on social media, I now understand why I am being asked. There are breeders spreading myths about the dilute gene. It is due to a lack of understanding and education; I get that, and I think they have good intentions of helping, but we also need to do our research. We are dog breeders in the genetics business, so we must educate ourselves correctly.
It's often claimed that dilute dogs are less healthy than those with black pigment. This misconception has come from the prevalence in some breeds of a condition known as Color Dilution Alopecia (CDA). Color Dilution Alopecia only affects the coat texture and length; not all breeds or dilute dogs are concerned. Most blues and Isabella are entirely healthy. As testing is not currently available, the best way to avoid CDA is to only breed dilute dogs with a regular coat.
Similarly, some breeders claim that dilute dogs should never be bred together. There is no genetic basis for this claim. Breeding healthy dilute to healthy dilute is the only way to reduce CDA in lines (until testing becomes available). Breeds that come only in dilute (e.g., Weimaraner) or have a very high incidence of dilute are far less likely to have CDA.
What do we know about dilution in Chihuahuas? We know that Chihuahuas carry d1 and d3; both cause the skin’s pigment to be gray/blue. Dilute, or blue does not refer to coat color but the skin color of the eye rims, nose, and paw pads. Currently, Embark Vet DNA only tests for Dilute 1; this is the dilute that is commonly associated with alopecia. Alopecia is easy to tell if it is an issue in long-coated chihuahuas. Usually, the ears are significantly affected. Lack of hair is a fault. In long-coated chihuahuas, so this is not desired. Alopecia is only a cosmetic issue and not life-threatening. Dilute three has only been related to Chihuahuas for a couple of years. We know that d3 is not associated with the alopecia issues that d1 has. Currently, U of C Davis is the only Lab testing for d3, and we have found that most of our blue dogs are d3, and many have unique coats. We have bred blue to blue for years, even d1 to d3, and had very positive results. A breeder questions if the dog's coat length is very thin or not up to the standard required, and they are d1. I would then ask my vet to do a skin scraping to see if alopecia is the issue.
How does dilution work on a genetic level in dogs?
The dilution gene occurs on the D locus. It is recessive, so d is dilute, and D is non-dilute, and for a dog to be cut, it must have the genotype dd. A dog with Dd or DD will have normal (non-dilute) pigment.
The dilution gene affects eumelanin (black and liver), although phaeomelanin (red) may also be lightened. When a dog has two copies of the d allele, a black dog will become blue (aka slate), and a liver (chocolate) dog becomes Isabella (aka lilac). A blue or Isabella can have any coat pattern, but whatever they have, any black or liver in the coat will be turned to blue or Isabella. It is genetically impossible for a blue dog to have any black in its skin or for an Isabella to have a liver.
The main giveaway that a dog is dilute is its nose color. The coat may be entirely sable or recessive red, for example, but if the dog has a blue nose, it is genetically blue-pigmented.
Lack dogs become blue when they are dd on the D locus. Blues can range from silver to slate or almost black, and it can be difficult to distinguish blue from black by looking at photographs. However, when the dog is examined, it should be evident that the nose is blue. Brindle stripes, tipping on a sable, masks, black patches on merles, saddles, patches on a black piebald, and the black on a tan-pointed dog will all be turned blue when a dog has the dilution gene. Any black hair on the dog is included. Sable tipping and merle patches may become challenging to see when diluted.