Coat colour White Spotting / Dominant White W21 (KIT-related) - Horse

What does this test analyse?

This genetic test analyses the KIT variant c.2369delC, known as W21. This variant belongs to the white spotting or dominant white series in horses. In practice, names such as dominant white, white spotting, sabino-like white, Camarillo White, tobiano or splashed white can sometimes be used for visually similar patterns, while different genetic variants may be involved.

W21 is especially relevant for Icelandic horses. W21 usually causes a predominantly white face with flecks and irregular white patches, especially visible on legs and belly. The final amount of white is not determined by this variant alone: base colour, other white-pattern genes and combinations with other KIT variants can strongly influence the visible coat pattern.

What does this W variant mean?

KIT is important for the development and migration of pigment cells. When a W variant changes KIT function, parts of the skin and hair follicles may receive too few pigment cells. This can produce white markings, white patches or, in some lines, almost completely white horses with pink skin under the white hair.

Practical value of this test

• Breeders can determine whether a horse can pass this specific W variant to its offspring.
• The test helps explain whether white markings or a dominant white pattern are caused by this variant or whether other loci should be investigated.
• For breeding plans, the result can be combined with other colour tests to estimate foal colour and amount of white more realistically.
• For sale, registration and communication with buyers, a DNA result gives more certainty than appearance or pedigree alone.
• The result helps plan matings between horses with white-pattern variants more deliberately, especially when a homozygous state may be undesirable or biologically unusual.

Inheritance and result

The result is reported as N/N, N/W21 or W21/W21. N/N means that the tested variant was not detected. N/W21 means that the horse carries one copy and can pass the variant on. W21/W21 means that two copies of this specific variant were detected. In Icelandic horses this pattern is also referred to as ýruskjóttur.