Dun is a dominant gene that dilutes the color of body hair, leaving the points and head unaffected. Dun horses also show 'primitive markings' consisting of a dark dorsal stripe, leg barring, shoulder stripes and concentric marks on the forehead (spiderwebbing, cobwebbing). The dorsal stripe appears to be a consistent feature of dun horses while the other 'primitive marks' vary and may not all be present, or visible. The effect of the Dun gene on the base colors of chestnut, bay and black produces horses with shades that range from apricot, golden, dark gray, olive, and many, more subtle, variations. Dun is inherited independently of other coat color genes and can occur in combination with any other genes that modify the base colors.

The specific mutation that causes Dun has not yet been identified, and there is no direct test for the gene. VGL has identified DNA markers associated with Dun that can be used to determine if a horse has the Dun gene and how many copies.

Explanation of Results:

• Horses with nd2/nd2 genotype will not be dun dilute and will not have primitive markings. They cannot transmit a dun dilution variant to their offspring.
• Horses with nd1/nd2 genotype will not be dun dilute, but may have primitive markings. They may transmit the non-dun 1 variant to 50% of their offspring.
• Horses with nd1/nd1 genotype will not be dun dilute, but may have primitive markings. They will transmit the non-dun 1 variant to all of their offspring.
• Horses with D/nd1 or D/nd2 genotype will be dun dilute and will display primitive markings. They may transmit the dun dilute variant to 50% of their offspring. Matings with N/N genotype will results in a 50% chance of producing a dun dilute foal.
• Horses with D/D genoytpe will be dun dilute and will transmit the dun dilute variant to all of their offspring. Matings with any genotype are predicted to produce dun dilute offspring.