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Extension | Chestnut (Base colour E-Locus Horse)

Three base colours occur in the horse: Chestnut (reddish), Black and Bay (Brown).The base colour is determined by the combination of the Extension locus (E) and Agouti locus (A).

 

The Extension locus (E) controls the production of the black pigment 'eumelanin' in the melanocytes.

If the gene is altered and non-functional (ee), the black pigment cannot be produced and the horse has a chestnut coat colour. Horses with one or two intact copies of the extension gene (EE, Ee) are either bay or black (depending on the Agouti gene).

General Information

  • The Extension gene controls the production of the black color pigment 'eumelanin' in the melanocytes.
  • If the gene is altered and non-functional (ee), the black pigment cannot be produced → the horse has a chestnut coat colour.
  • Horses with one or two intact copies of the extension gene (EE, Ee) are either bay or black (depending on the Agouti locus).

Genotype and Lab Report

Inheritance: autosomal recessive

→ Horses with two copies of this variant (e/e) are chestnut (red, sorrel) in colour. Horses with only one copy of this variant (E/e) are bay or black (depending upon their variants at the Agouti locus), but carry chestnut. A horse that does not carry the variant (E/E) cannot have a chestnut foal, even if bred to a chestnut horse.

 

Genotype

 

E/E = Two functional copies

The horse is bay or black, depending on the A locus.

 

E/e = One functional and one non-functional copy

The horse is bay or black, depending on the A locus. It carries one copie of chestnut.

 

e/e = Two non-functional copies

The horse has a chestnut coat colour, independent of the A locus.

Appearance

Chestnut

Sorrel to red base colour over the entire body. Sometimes with lighter main and tail.

 

Possible genotypes:

 

  • eeAA = Homozygous for Bay
  • eeAa = Carrier of Bay
  • eeaa = Homozygous for Black

Black

Black base colour over the entire body.

 

Possible genotypes:

 

  • EEaa = Homozygous Black
  • Eeaa  = Carrier of Chestnut

Bay

Brown base colour over the body with black main, tail and legs.

 

Possible genotypes:

 

  • EEAA = Homozygous Bay
  • EeAA = Carrier of Chestnut
  • EeAa = Carrier of Chestnut and of Black
  • EEAa = Carrier of Black

Test Information

Locus Informationen: E-Locus

 

This test detects two mutations (c.248C>T und c.250G>A) in the MC1R gene.

Literature

Marklund, L., Moller, M.J., Sandberg, K., Andersson, L.: A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses. Mammalian Genome 7:895-899, 1996. Pubmed reference: 8995760.

 

Wagner, H.J., Reissmann, M.: New polymorphism detected in the horse MC1R gene. Anim Genet 31:289-90, 2000. Pubmed reference: 11086549.

 

Further information is available at Online Mendelian Inheritance in Animals.

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