Genetics

Isabella and Lilac Dogs: The Double Dilute Color Genetics

Isabella and lilac are the same thing — a silver-fawn color produced when chocolate and dilution combine. Here's the genetics behind one of the rarest dog colors.

June 3, 2024 · 4 min read

What Creates Isabella/Lilac

Isabella (also called lilac in some breeds) occurs when a dog is homozygous recessive at both the B locus (bb = chocolate) and the D locus (dd = dilution). The chocolate gene converts black pigment to brown; the dilution gene then further lightens that brown to a pale silver-fawn called isabella. In nose leather, eye rims, and paw pads, the color appears as a pale lavender-grey rather than black or brown.

The Genotype Required

An isabella dog must be bb/dd — two recessive b alleles AND two recessive d alleles. Both parents must carry at least one copy of each recessive allele for isabella offspring to be possible. The probability of producing an isabella puppy from two double carriers (Bb/Dd × Bb/Dd) is approximately 1/16 — making it genuinely rare from properly health-tested parents who are not being specifically selected for this color.

Health Considerations

Isabella dogs combine the health risks of the D locus (color dilution alopecia risk) with any breed-specific health risks. In French Bulldogs specifically, isabella-colored dogs are often produced through intensive selective breeding that can compromise genetic diversity. As with all rare color breeding, prioritizing color over health testing and structural soundness is a significant concern with isabella breeding programs.