Mushroom is a unique recessive coat color type found in the Shetland Pony. Horses with two copies of Mushroom dilution are typically described as being a sepia color, and may also have a light or flaxen mane and tail.
In 2019, researchers used 12 Mushroom colored horses to map the phenotype to a frameshift mutation in MFSD12 on equine chromosome 7. This recessive dilution gene that affects red pigment in horses. Mushroom is a unique coat color phenotype found primarily in the Shetland Pony and Miniature Horses. Because Mushroom dilution only affects red pigment, black- or bay-based horses will not express the Mushroom pigmentation. These horses can still pass on the gene mutation to any offspring.
Jocelyn Tanaka, Tosso Leeb, James Rushton, Thomas R. Famula, Maura Mack, Vidhya Jagannathan, Christine Flury, Iris Bachmann, John Eberth, Sue M. McDonnell, Maria Cecilia T. Penedo, Rebecca R. Bellone Genes (Basel) 2019 Oct; 10(10): 826. Published online 2019 Oct 19. doi: 10.3390/genes10100826 [PMCID: PMC6827053]
|Mu/Mu||Homozygous; Horse has two copies of the Mushroom Dilution gene mutation and will express the dilution on red or bay-based coats. Horse will pass a copy of Mu to all offspring.|
|n/Mu||Heterozygous; Horse is a carrier of the Mushroom Dilution gene mutation. Horse has a chance to pass this gene on to any offspring.|
|n/n||Negative; Horse is negative for the Mushroom Dilution gene mutation.|