Blue and Lavender Chihuahuas: How the Dilute Gene Really Works

Nov 29, 2022

7 min read

Updated: Oct 30

Examples of dilute Chihuahuas. All of these dogs have been DNA tested as d1, d3, or both.

By Rev. T. Stringer, Lead Researcher, SIPGS

Blue and lavender are some of the most asked-about looks in the breed.

They are also full of myths.

Here is what the DNA actually says.

Dilute is a pigment change, not a coat color

Like chocolate, dilute is not a coat color.

It changes the pigment the dog already makes.

A black-pigmented dog becomes blue.
A chocolate dog becomes lavender.

The pattern stays the same.

A blue dog can be blue fawn, blue and tan, blue brindle, solid blue, or blue spotted on white.

What makes a dog dilute

The gene is called MLPH (melanophilin), at the D locus.

MLPH helps move pigment out to the hair and skin.

In a normal dog, pigment is spread out evenly.

In a dilute dog, the pigment clumps together.

Clumped pigment looks lighter. Black looks blue. Brown looks lavender.

Dilute works mostly on the dark pigment (eumelanin).

It can also make fawn and cream a little paler.

Dilute changes the skin too

Dilute does not stop at the coat.

It changes every place the dark pigment shows:

Nose: slate blue-gray on a blue dog, pale taupe on a lavender dog.
Eye rims: match the nose.
Paw pads: match the nose.
Eyes: often pale amber, usually lighter than a chocolate dog's eyes.

Pro tip: check the nose first.

A fawn or cream dog with a blue-gray nose is a dilute dog, even with almost no blue hair.

Blue Chihuahua or lavender: the B locus decides

Genotype	Color
B/B or B/b, with d/d	Blue
b/b with d/d	Lavender

Lavender needs two separate genes:

b/b at the B locus makes the dark pigment brown.
d/d at the D locus dilutes it.

If a dilute dog has even one B, it is blue, not lavender.

In other breeds, lavender is often called Isabella or lilac.

In Chihuahuas, the term is lavender.

Dilute is recessive

A dog needs two dilute copies to be dilute.

Genotype	What you see	Breeding
D/D	Normal dark pigment	Cannot make dilute puppies
D/d	Normal dark pigment, carries dilute	Can pass dilute to about half of puppies
d/d	Dilute coat and skin	Passes dilute to every puppy

Breeding odds

Parents	Dilute puppies
D/D × anything	0%
D/d × D/d	about 25%
D/d × d/d	about 50%
d/d × d/d	100%

Two dark-pigmented parents can have a blue puppy.

That happens when both carry one dilute copy.

It did not "skip a generation." It was there all along, hidden.

The three dilute variants

Researchers have found three different broken versions of MLPH in dogs.

Variant	What changed in the gene	Found in
d1	A single letter change that disrupts how the gene is read	Many breeds. The most common dilute variant overall.
d2	A single letter change that swaps one building block of the protein	Chow Chow, Sloughi, Thai Ridgeback
d3	One extra letter that throws the gene out of frame	Chihuahua, Italian Greyhound, Yorkshire Terrier, Pekingese, Shih Tzu, and others

In Chihuahuas, we see d1 and d3.

The dogs pictured in this post have all been DNA tested as d1, d3, or both.

Any two dilute variants together make a dilute dog.

d1/d1, d1/d3, and d3/d3 all look the same.

What happens if you breed d1 to d3?

This is one of the most common questions we get.

The short answer: d1 and d3 act the same.

A puppy that gets any two dilute copies is dilute.

It does not matter which ones.

Two dilute parents: d1/d1 × d3/d3

Every puppy gets d1 from one parent and d3 from the other.

Puppies	Result
100% d1/d3	Dilute

Two carriers: D/d1 × D/d3

Puppies	Result
about 25% D/D	Not dilute, carries nothing
about 25% D/d1	Not dilute, carries d1
about 25% D/d3	Not dilute, carries d3
about 25% d1/d3	Dilute

A dilute to a carrier: d1/d1 × D/d3

Puppies	Result
about 50% D/d1	Not dilute, carries d1
about 50% d1/d3	Dilute

A d1/d3 puppy looks the same as a d1/d1 or d3/d3 puppy.

The shade does not change.

That puppy will pass either d1 or d3 to each of its own puppies.

There may be more dilute variants

Most major labs now test for d1, d2, and d3.

But researchers suspect there are more dilute variants that have not been found yet.

Some dogs look dilute, with a blue-gray nose and pads, but test D/D for all three known variants.

Breeder tip: if the nose says dilute and the test says D/D, trust the nose.

That dog likely carries a dilute variant no test can find yet.

Breed it as a dilute, and let your lab know. Cases like these are how new variants get found.

It is all or nothing

A d/d dog cannot have any true black or true brown pigment.

Every dark hair is diluted.

If you see true black anywhere, in brindle stripes, sable tips, tan-point markings, or on the nose, the dog is not dilute.

Born blue vs. greying

Some dogs turn gray as they age but are not dilute.

True dilute ("born blue")

Dilute from birth.
The color stays the same for life.
Nose, eye rims, and pads are diluted.

Greying genes (not dilute)

Born black or chocolate, with dark pigment.
The coat fades to gray as the dog matures.
The nose stays black or brown. That is the giveaway.

Progressive greying is well known in breeds like Kerry Blue Terriers, Poodles, Bearded Collies, and Old English Sheepdogs.

In Chihuahuas, a gray dog with a blue nose is a true dilute.

Dilute and health: color dilution alopecia (CDA)

CDA is a skin and coat condition seen in some dilute dogs.

It causes thinning hair and hair loss, mostly on the body.

It can also bring dry, flaky skin and repeat skin infections.

It usually starts between a few months and a few years of age.

A common early sign: thin or missing hair on the back of the ears.

If a dilute dog has bare patches there, take it to your vet for a skin biopsy.

What we know:

CDA is seen in Chihuahuas. It is also seen in blue French Bulldogs, blue Dobermans, and dilute Labradors.
It is cosmetic. It affects the skin and coat. Dogs with CDA still live long lives.
Not every d/d dog gets CDA. Many dilute dogs have normal coats for life.
Some all-dilute breeds rarely have it. Classic Weimaraner lines are all dilute, and CDA does not appear to affect them. The same is true for blue Great Danes.
There is no test for CDA itself. A D locus test tells you if a dog is dilute. It cannot tell you if that dog will get CDA.
Diagnosis takes a skin biopsy.

Because all-dilute breeds can be free of CDA, being dilute alone does not cause it.

Other genes in a line likely play a part.

A dog with CDA can live a full, happy life as a pet.

It is not considered ethical to breed a dog with CDA.

Breeding dilute to dilute

Some breeders say dilutes should never be bred together.

The genetics do not support that rule.

The Weimaraner shows that a breed can be all dilute and still be free of CDA.

What matters most is the dogs, not the color pairing.

Good practice:

Do not breed a dog with CDA.
Breed only dilutes with healthy skin and full coats.
Watch puppies and adults for any coat or skin problems, especially thin hair on the back of the ears.
Know every breeding dog's D locus result, including d3.

Some breeders choose dilute to carrier for diversity. Others choose dilute to dilute.

Both can be responsible when the dogs are healthy.

How to read a D locus test result

Result	What it means	Can pass dilute?
D/D	No tested dilute variants found	No (for the variants tested)
D/d	Carries one dilute variant	Yes, to about half of puppies
d/d	Dilute	Yes, to every puppy

Three things to check:

Does the result match the nose? If not, check which variants were tested.
Were d1, d2, and d3 all tested? And remember, a D/D dog with a dilute nose may carry a variant not yet known.
Check the B locus too. A d/d dog that is also b/b is lavender, not blue.

Key takeaways

Dilute is a pigment change, not a coat color.
It comes from the MLPH gene at the D locus, and it is recessive (d/d).
Black becomes blue. Chocolate becomes lavender.
Nose, eye rims, and pads are diluted too. Check the nose first.
Three dilute variants are known so far. Chihuahuas carry d1 and d3.
d1 × d3 works like any other dilute pairing. Two dilute copies of any kind make a dilute puppy.
Most labs test d1, d2, and d3, but more dilute variants are suspected. Trust the nose.
CDA is seen in Chihuahuas. It is cosmetic, and affected dogs still live long lives.
Not every dilute dog gets CDA, and all-dilute breeds can be free of it.
Dogs with CDA should not be bred.
There is no DNA test for CDA. Breed healthy-coated dilutes and watch your lines.

Sources

Drögemüller C, Philipp U, Haase B, Günzel-Apel AR, Leeb T. (2007). A noncoding melanophilin gene (MLPH) SNP at the splice donor of exon 1 represents a candidate causal mutation for coat color dilution in dogs. Journal of Heredity, 98(5):468-473.
OMIA 000031-9615: Coat colour, dilution, MLPH-related in dogs. Online Mendelian Inheritance in Animals, University of Sydney. Lists d1 (Drögemüller et al., 2007), d2 (Bauer et al., 2018), and d3 (Van Buren et al., 2020), with the breeds each is found in.
UC Davis Veterinary Genetics Laboratory. Dilute (D Locus/Blue) test information.
Laboklin. Colour dilution alopecia: breeds, onset, and testing limits.

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