Mushroom Dilution

Animal Genetics > Horse Tests > Equine Color Tests > Mushroom Dilution
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Description

Mushroom is a recessive dilution that affects red pigment, producing a distinctive sepia or taupe coat, often with a lighter or flaxen mane and tail. It is found primarily in Shetland Ponies and Miniature Horses.

In 2019, researchers mapped the Mushroom phenotype in a group of Mushroom-colored ponies to a frameshift variant in the MFSD12 gene on equine chromosome 7. Mushroom is inherited recessively, so only horses with two copies of the variant (Mu/Mu) show the dilution.

Because Mushroom acts on red pigment, it visibly dilutes chestnut-based horses. Black-based horses do not show the Mushroom phenotype even when they carry two copies, and horses with one copy (n/Mu) look normal regardless of base color. Carriers can still pass the variant to their offspring, so two carriers bred together have a 25% chance of producing a Mushroom foal.

DNA testing identifies carriers that cannot be recognized by eye, which is useful for breeders working with the color or wanting to know what colors a mating could produce. Because the visible effect depends on the base coat, this test is most informative alongside the Red/Black Factor test.

Possible results

Genotype Description
Mu/Mu Homozygous: Horse has two copies of the Mushroom Dilution variant and will express the dilution on a red-based coat. Horse will pass one copy to all offspring.
n/Mu Heterozygous: Horse is a carrier of the Mushroom Dilution variant but does not express the dilution. Each foal has a 50% chance of inheriting it.
n/n Negative: Horse does not carry the Mushroom Dilution variant.

Breeds Affected

Shetland Pony, Miniature Horse

Reference

Frameshift variant in MFSD12 explains the mushroom coat color dilution in Shetland ponies.

Tanaka J, Leeb T, Rushton J, Famula TR, Mack M, Jagannathan V, Flury C, Bachmann I, Eberth J, McDonnell SM, Penedo MCT, Bellone RR.
Genes (Basel). 2019 Oct 19;10(10):826. doi: 10.3390/genes10100826.
PMID: 31635130

Related Tests

  • Red/Black Factor — shows whether the horse has the red pigment mushroom acts on
  • Silver Dilution — common in the same breeds and also produces a flaxen mane and tail
  • Cream Dilution — another dilution to rule out on a lightened coat

Breeding Shetlands or Miniatures? The Shetland Pony & Miniature Horse Color Panel includes mushroom plus seven other color tests for $75.