Dun: a lighter body with dark markings

Recognize the whole pattern

Dun lightens much of the body while keeping more pigment in areas such as the mane, tail and lower legs. A dark stripe along the back is typical. Leg bars, shoulder markings and marks on the forehead vary; together they are often called primitive markings.

The inherited base still shows through the effect: chestnut gives red dun, bay gives bay dun and black gives grullo. Traditional names differ among breeds, so describing both the base and the dilution avoids confusion.

Sources for this explanation [1] · [2]

What happens inside a colored hair

TBX3 is the scientific symbol for the gene involved. The gene is active in parts of the hair follicle, where hair grows, and helps distribute pigment unevenly around each hair. This uneven distribution makes much of the body look lighter.

The non-dun versions change how the gene is controlled in the follicle, producing more evenly pigmented hairs. This is a change within the colored hair, rather than a mixture of white and colored hairs.

Sources for this explanation [1] · [2]

What D, nd1 and nd2 mean

These letters name three alleles, or versions of the gene region. D produces Dun dilution. One D is enough, so D/D, D/nd1 and D/nd2 are Dun combinations.

Without D, nd1/nd1 and nd1/nd2 can retain primitive markings without Dun body dilution. nd2/nd2 lacks this dilution and the primitive markings associated with this region. A photograph of a stripe or ordinary dark shading cannot, by itself, distinguish these possibilities.

Sources for this explanation [1] · [2]

Example and limits of the test

For a tested D/nd2 parent crossed with nd2/nd2, every foal has a 50% chance of D/nd2 and 50% of nd2/nd2. A D/D parent always passes D. These probabilities concern each conception, not an alternating sequence of foals.

Testing distinguishes the inherited combinations but does not predict every marking or its intensity. Cream can occur together with Dun, so a horse may have both dilutions.

Sources for this explanation [1] · [2]

Where the explanations come from

Laboratory resources explain which variants are tested and how to read their results. Research papers describe the evidence, discoveries and remaining uncertainties. Each article links its explanations to the relevant sources. Published titles stay in their original language so you can find the exact work.

1. 1 · Laboratory explanation

   UC Davis VGL — Dun Dilution

2. 2 · Research paper

   Imsland et al. (2016) — TBX3 and Dun camouflage colour