• About This Guide
  
• How This Guide is Being Developed
  
• Philosophy of this guide
  
• Using this Guide
  
• Thinking Scientifically
  
• About the Author
  
• Documented Genes
  
• What is a documented gene?
  
• Black/Red (MC1R)
  
• Bay (ASIP)
  
• Cream/Pearl (SLC45A2)
  
• Dun (TBX3)
  
• Gray (STX17)
  
• Silver (PMEL17)
  
• Champagne (SLC36A1)
  
• Roan/Tobiano/Sabino/White Spotting (KIT)
  
• Splash White (MITF/PAX3)
  
• Leopard Complex (TRPM1/ECA3P)
  
• Frame (EDNRB)
  
• Tiger Eye (SLC24A5)
  
• Height Regulation (HMGA2/LCORL)
  
• Mushroom (MFSD12)
  
• Hypothetical Genes
  
• What is a hypothetical gene?
  
• Borrowed Genes
  
• Glossaries
  
• Glossary of Colors
  
• Glossary of Terms
  

Black/Red (MC1R)

• Last updated: 2026-01-13

  Common Names: Black/Red Gene, Extension 

  Scientific Name: Melanocortin 1 receptor (MC1R)

  Equine Chromosome: 3

  General Overview:

  The E gene (E for extension), controls if a horse can produce black and red pigment or only red pigment. [1]
  
  Horses with E/E or E/e genotypes produce both red and black pigment types. They come in colors like black, bay, brown, grullo, silver dapple, buckskin etc. E/E horses can never produce a red foal. 

  
  

  Horses with e/e genotypes produce only red pigment. They come in colors like chestnut, sorrel, red dun, palomino, red roan etc.

  
  

  A third very rare form of this gene is known in horses. e^a is found in Black Forest, Knabstrupper and Canadian horses. It is functionally identical to the more common e form. e^a is not currently found in HorseGeneticsGame.com.

• Citations:

  1. Marklund L et al., “A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses.” (1996) Mamm Genome. 7: 895-9. https://link.springer.com/article/10.1007/s003359900264 
  2. Wagner, H-J & Reissmann, Monika. (2000). New polymorphism detected in the horse MC1R gene. Animal genetics. 31. 289-90. 10.1046/j.1365-2052.2000.00655.x.  https://www.academia.edu/23895066/New_polymorphism_detected_in_the_horse_MC1R_gene

• Examples:

  Black and Bay horses showing the E allele

  

  
  

  Chestnut horse showing the e allele