• 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
  

Philosophy of this guide

• Last updated: 2026-01-24

  
  

  This guide is primarily written to help the members of HorseGeneticsGame.com with breeding their horses in game. I hope that the information presented here will be usable both to those who play HGG and those that do not. With that in mind I will be writing with a focus on real life science instead of how things are done in game. When information is specific only to the game or does not apply to the game it will be labeled as such. 

  
  

  This guide seeks to take a scientific approach rather than a dogmatic one. That means the information given is never taken as an absolute truth but instead it should be viewed as the most accurate information as it is understood at the time of writing. The information presented will always include citations so you can read the information yourself, and will label conjecture when it is presented.  

  
  

  This guide seeks to understand equine genetics in the larger context of all mammalian genetics. Almost all genes are shared between mammal species and what is learned from one species helps inform the bigger picture of what is going on with another. 

  
  

  This is a living document, that means it will be updated as scientific knowledge develops over time or as clarification is needed. The information presented in this guide will inevitably have errors, both because no one person can know everything but also because genetics is a science that is ever developing. If you have corrections or new information to share I would love to see it. I just ask that you provide a peer reviewed source and share it in a kind manner. There is no reason why we can not all seek knowledge together. 

• Terminology

  This guide aims to help the reader stop thinking of color genetics like cars slotting into garage bays, and to instead think about it like typos in a book. You can keep accumulating typos but eventually whole passages of the book may no longer make sense. With this in mind this guide will often use the term mutation as a reminder that there is an error in this version of that gene.

  
  

  It is more technically correct to say allele, as that term means the whole of the gene, inclusive of any mutations we are discussing. Many geneticists will also use the terms polymorph or haplotype in a similar way to allele. The specific nuances between each of these terms isn't vital for the lay learner to understand. Just know that you will see the terms mutation and allele both in this guide and in both cases I am talking about a specific variant of that gene.