hat are the three testable variants of the D allele?

The three testable variants of the recessive d allele are d1, d2, and d3.

While current genetic tests can successfully identify these three specific variants to confirm whether a dog carries the dilute trait, they cannot predict whether a dog with the dilute genotype will actually develop Colour Dilution Alopecia (CDA). Researchers suspect that other variants of the d allele exist, but they have not yet been identified.