How do researchers identify the d1, d2, and d3 variants?

Researchers identify the d1, d2, and d3 variants of the recessive d allele (located on the MLPH gene) using diagnostic DNA tests.

While these genetic tests can successfully detect these three specific variants (with d1 being the standard D-locus variant, and d2 and d3 considered “rare” variants) to confirm if a dog carries the dilute trait, current tests cannot predict whether a dog with the dilute genotype will actually go on to develop Colour Dilution Alopecia (CDA). Researchers also suspect that other variants of the d allele exist, but they have not yet been identified or developed into testable markers.