• 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 (MATP)
  
• 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)
  
• Glossaries
  
• Glossary of Colors
  
• Glossary of Terms
  

About This Guide

How This Guide is Being Developed

• Last updated: 2026-01-14

  
  

  This guide is in the process of being written, and I expect it to take at least all of 2026 to get the core parts of it finished. I expect it to always be evolving as more information is published. I apologize in advance if you run into unfinished sections. If you have an area you would like me to focus on finishing, or want me to expand on, please let me know.

  Here are my current progress goals:

  1. Complete the overview of all documented genes.
  2. Complete the overview of all hypothetical and fantasy genes.
  3. Complete the overview of non standard expression
  4. Complete the Glossary of Colors
  5. Complete the overview of genetic disorders
  6. Write up in-depth information about the functioning of documented gene
  
  

  I am also looking to expand the Glossary of Terms as I find new ones that need to be added. The in-depth knowledge write ups will probably also be done throughout the process as the mood strikes me. These will be the most complex and intense parts of the guide so spacing them out will help prevent burn out. 

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.

  
  

Using this Guide

• Last updated: 2026-01-14

  This guide is divided into Documented Genes, Hypothetical Genes, Fantasy Genes, Genetic Disorders and Nonstandard Expression. Documented genes have been identified by geneticists and their location published in academic papers. Often testing is available for these genes. 

  
  

  Hypothetical genes range from well supported genes that almost certainly exist in horses but have not been documented yet, to unsupported genes which almost certainly do not exist in horses but could theoretically be possible using genetic engineering. Fantasy genes are scientifically impossible genes found in HorseGeneticsGame.com and are not intended to reflect any real life genes.

  
  

  Genetic Disorders are found in real life horses and are important for all horses lovers to be educated on but are not found in HorseGeneticsGame.com. Nonstandard expression includes somatic mutations, brindle and other oddities.

  
  

  If you are a HGG member all of the categories except Genetic Disorders are useful for you to be acquainted with. If you are looking to learn about real horses the Documented and Genetic Disorders categories are the most important to learn about, with the Well Supported Hypothetical Genes also being very useful to learn.

Thinking Scientifically

• Last updated: 2026-01-14

  What makes thinking dogmatic?

  An idea is dogmatic when it is applied with rigid certainty, often because an authority figure, or peers said it was the truth. When someone is thinking dogmatically they don't apply a spirit of critical enquiry to information they have learned. They don't question the biases or larger context of the information. That information might still be true. The way of thinking about something does not make it true or false. However, rigid dogmatic thinking is the opposite of scientific thinking.

  
  

  What makes thinking scientific?

  Scientific thinking weighs the data presented against previously gathered evidence, applies careful observation, and most importantly revises its conclusions as new data is presented. We should all strive to approach genetics as a science that is ever growing and evolving in knowledge and never as a universal truth to be applied. Be weary of those who insist something is true without providing evidence and sources.

About the Author

• Last updated: 2026-01-14

  This guide is written by Ellie Akers, also known as Ammit, the creator of HorseGeneticsGame.com. Ellie is a well educated lay person but not a geneticist. Ellie started her first genetic experiments in 4th grade by breeding a population of purple striped starflowers from all white original stock, in her backyard. Once she learned about horse genetics young Ellie was hard at work organizing her toy horses into genetically plausible families.  Ellie has been studying horse genetics as a hobby for over 30 years and has studied inheritance first hand while breeding horses, goats, ducks, chickens, and of course plants. 

Documented Genes

What is a documented gene?

• Documented genes have been studied and identified by geneticists and published in a peer reviewed journal. These genes have been proven to exist in horses.

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

  

  
  

Bay (ASIP)

• Last updated: 2026-01-14

  Common Names: Bay, Agouti 

  Scientific Name: agouti signaling protein (ASIP)

  Equine Chromosome: 22

  General Overview:

  The A gene (A for agouti) is responsible for controlling the distribution of black and red pigment. A horse must have at least one copy of dominant E for agouti to have any effect. [1] Horses with A/A or A/a and having at least one copy of dominant E, will have some amount of restriction of black pigment. This can range from nearly all black in the case of dark brown horses, to nearly no black pigment in the case of wild bay horses.
  
  Horses with the recessive a/a genotype, and having at least one copy of dominant E, will show no pheomelanin (red) pigment.
  
  Agouti status has no impact on e/e horses. 

  
  

  An older, now discredited idea, proposed that the wide variety of shades of bay was influenced by different polymorphs of the A gene. A^t was proposed for brown shades and A⁺ for wild bay shades. There is now strong evidence that the combined status of E and A play a large role in determining the final shade. [2] My own conjecture is that additional genetic and environmental factors almost certainly play a role in deciding the final shade as well.

• Citations:

  1. Rieder, S., Taourit, S., Mariat, D., Langlois, B., & Guérin, G. (2001). Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus). Mammalian Genome, 12(6), 450-455. doi: https://pubmed.ncbi.nlm.nih.gov/11353392/ 

   

  2. Shang S, Yu Y, Zhao Y, Dang W, Zhang J, Qin X, Irwin DM, Wang Q, Liu F, Wang Z, Zhang S, Wang Z. Synergy between MC1R and ASIP for coat color in horses (Equus caballus)1. J Anim Sci. 2019 Apr 3;97(4):1578-1585. doi: 10.1093/jas/skz071. PMID: 30785190; PMCID: PMC6447268. https://pubmed.ncbi.nlm.nih.gov/30785190/

• Examples:

  A range of bay expression from light to very dark

  

  
  

  

Cream/Pearl (MATP)

• Last updated: 2026-01-14

  Common Names: Cream, Pearl, Sunshine, Snowdrop

  Scientific Name: solute carrier family 45 member 2 (SLC45A2) or Membrane-associated transporter protein (MATP)

  Equine Chromosome: 21

  General Overview:

  The cream mutation of SLC45A2, often noted as Cr, is an incompletely dominant dilution gene that reduces pigmentation in the eyes and coat. [1] One copy of cream has a moderate dilution effect that turns red pigment into shades of gold and buff. It has minimal to no visible effect on black pigment [2]. One copy of cream, turns black horses smoky black, bays into buckskins and chestnuts into palominos.
  
  When two copies of the cream mutation are present there is significant reduction in both black and red pigment resulting in cream colored horses with blue eyes and pink skin.[1] Two copies turn black horses into smoky creams, bays into perlinos, and chestnuts into cremellos. 

  
  

  Pearl is another mutation located on SLC45A2, often marked as Prl. Pearl dilutes both red and black pigment equally, but to a much lesser degree than cream. [3] One copy results in a horse with normal coloration but may have very slight dilution or skin mottling. [4] Two copies of pearl produce a uniform apricot color with paler than normal skin. Eyes tend to be amber to green in hue. [3]

  
  

  Sunshine (C^sun) is a pearl-like dilution of SLC45A2. It has no known impact when heterozygous and produces a pearl-like appearance when homozygous. This mutation is only known from one line of Standardbreds. [5]

  
  

  Snowdrop (C^sno) is a recessive dilution of SLC45A2. It has no visible effect when heterozygous, and produces a pseudo double cream appearance when homozygous. This mutation is only known from one line of Vanner horses. [6]

  
  

  All known mutations of SLC45A2 amplify one another. When combined they often produce cream colored coats, with pink skin and blue eyes.

• Citations:

  1. Mariat D, Taourit S, Guérin G. A mutation in the MATP gene causes the cream coat colour in the horse. Genet Sel Evol. 2003 Jan-Feb;35(1):119-33. doi: 10.1186/1297-9686-35-1-119. PMID: 12605854; PMCID: PMC2732686. https://hal.science/hal-00894438v1/file/hal-00894438.pdf
  2. “Cream | Veterinary Genetics Laboratory.” Vgl.ucdavis.edu, vgl.ucdavis.edu/test/cream
  3. Sevane N, Sanz CR, Dunner S. Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses. Anim Genet. 2019 Jun;50(3):275-278. doi: 10.1111/age.12784. Epub 2019 Apr 10. PMID: 30968968. https://www.ucm.es/data/cont/docs/345-2019-04-11-... 
  4. Sponenberg D.P. & Bellone R. (2017) Equine Color Genetics, 4th edn. John Wiley & Sons, Hoboken, NJ.
  5. Holl HM, Pflug KM, Yates KM, Hoefs-Martin K, Shepard C, Cook DG, Lafayette C, Brooks SA. A candidate gene approach identifies variants in SLC45A2 that explain dilute phenotypes, pearl and sunshine, in compound heterozygote horses. Anim Genet. 2019 Jun;50(3):271-274. doi: 10.1111/age.12790. Epub 2019 Apr 21. PMID: 31006892.
     https://onlinelibrary.wiley.com/doi/10.1111/age.12790
  6. Bisbee D, Carpenter ML, Hoefs-Martin K, Brooks SA, Lafayette C. Identification of a novel missense variant in SLC45A2 associated with dilute snowdrop phenotype in Gypsy horses. Anim Genet. 2020 Mar;51(2):342-343. doi: 10.1111/age.12913. Epub 2020 Jan 21. PMID: 31961951. https://www.researchgate.net/publication/337464050... 

• Examples:

  Bay E/? a/a -/-, Smoky Black E/? a/a Cr/-, Smoky Cream E/? a/a Cr/Cr

  

  
  

  Bay E/? A/? -/-, Buckskin E/? A/? Cr/-, Perlino E/? A/? Cr/Cr

  

  
  

  Chestnut e/e -/-, Palomino e/e Cr/-, Cremello e/e Cr/Cr

  

  
  

  Black Pearl Carrier E/? a/a Prl/-, Black Pearl E/? a/a Prl/Prl, Smoky Black Pearl E/? a/a Prl/Cr

  

  
  

  Bay Pearl Carrier E/? A/? Prl/-, Bay Pearl E/? A/? Prl/Prl, Buckskin Pearl E/? A/? Prl/Cr

  

  
  

  Chestnut Pearl Carrier E/? Prl/-, Chestnut Pearl E/? A/? Prl/Prl, Palomino Pearl E/? A/? Prl/Cr

  

  
  

Dun (TBX3)

• Last updated: 2026-01-14

  Common Names: Dun

  Scientific Name: T-box transcription factor 3 (TBX3)

  Equine Chromosome: 8

  General Overview:

  The TBX3 gene has three known forms in horses. Dun (D), non-dun 1 (nd1) and non-dun 2 (nd2). Dun is believed to be the more ancient form of the gene. Non-dun 1 is a mutation that results in less diluted pigment and less primitive markings than dun. Non-dun 2 is an additional mutation that happened on the non-dun 1 variant to produce a version with no dilution and primitive markings at all. [1]

  
  

  Dun is the most dominant form. Dun turns black horses grullo, bays into bay duns and chestnuts into red duns. Dun dilutes the body color of the horse, to a more buff, tan, mousy or golden tone than the original color. Dun horses normally have darker faces, legs, manes, and tails than their body colors. They will have a distinctly darker dorsal stripe running the full length of their spine and darker bars on their ears. Many duns have additional "primitive markings” like forehead cobwebs, shoulder capes or stripes, and leg barring.

  
  

  Non-dun 1 is the next most dominant. It results in very minimal body dilution that may not be discernible from normal coloration by eye. Non-dun 1 horses normally have the suggestion of a dorsal stripe which is not as clear as true dun dorsal stripes.

  
  

  Non-dun 2 is the least dominant. This is the typical coloration and causes no dilution or primitive markings.

  
  

• Citations:

  1. Imsland, Freyja & McGowan, Kelly & Rubin, Carl-Johan & Henegar, Corneliu & Sundström, Elisabeth & Berglund, Jonas & Schwochow, Doreen & Gustafson, Ulla & Imsland, Páll & Lindblad-Toh, Kerstin & Lindgren, Gabriella & Mikko, Sofia & Millon, Lee & Wade, Claire & Schubert, Mikkel & Orlando, Ludovic & Penedo, Cecilia & Barsh, Gregory & Andersson, Leif. (2015). Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nature Genetics. 48. 10.1038/ng.3475. https://pubmed.ncbi.nlm.nih.gov/26691985/

• Examples:

  Grullo E/? a/a D/?, Bay Dun E/? A/? D/?, Red Dun e/e D/?

  

  
  

  Black with nd1 E/? a/a nd1/?, Bay with nd1 E/? A/? nd1/?, Chestnut with nd1 e/e nd1/?

  

  
  

Gray (STX17)

• Last updated: 2026-01-14

  Common Names: Gray

  Scientific Name: Syntaxin-17 (STX17)

  Equine Chromosome: 25

  General Overview:

  The gray mutation causes hyperpigmentation (excessive amounts of pigment). Foals are born darker than normal, and will progressively develop white hair with age. Gray is caused by a duplication in the STX17 gene, resulting in two copies of the gene being found on one chromosome (G2 for gray 2). Many gray lines have an additional duplication of this gene resulting in three copies of the gene on a single chromosome (G3 for gray 3). [1]

  
  

  The more duplications a horse has the faster they will turn white and the higher their risk of cancer.[2]

  
  

  Fleabites are caused by areas of pigment reactivating as a horse ages. They are almost always found on heterozygous gray horses and are more common in G2 lines and heterozygous individuals. [2]

  
  

  Bloodmarks are large areas where the gray gene was delayed in activating. They tend to be visible from a young age and will often gray eventually just at a much reduced rate. My personal conjecture is these are probably caused by areas where one of the STX17 duplications was disabled early on during embryonic development. Effectively a somatic mutation.

  
  

  Chubari spots are large coin sized circular areas that gray faster than other areas.

  
  

  HorseGeneticsGame.com currently only uses one gene to represent gray.

• Citations:

  1. Rubin, CJ., Hodge, M., Naboulsi, R. et al. An intronic copy number variation in Syntaxin 17 determines speed of greying and melanoma incidence in Grey horses. Nature Communications 15, 7510 (2024). doi: 10.1038/s41467-024-51898-2
  2. Andersson L. White horses - non-coding sequences drive premature hair greying and predisposition to melanoma. Ups J Med Sci. 2024 Apr 2;129. doi: 10.48101/ujms.v129.10626. PMID: 38571883; PMCID: PMC10989212. https://pmc.ncbi.nlm.nih.gov/articles/PMC10989212/

Silver (PMEL17)

• Last updated: 2026-01-13

  Common Names: Silver, Silver Dapple, Taffy

  Scientific Name: Premelanosome protein 17 (PMEL17)

  Equine Chromosome: 6

  General Overview:

  The silver gene dilutes black pigment into a chocolatey brown color. Chestnut horses will have no coat color effect. [1] Silver black horses can range from silver to dark chocolate in color with lightened manes and tails. They are sometimes mistaken for sooty palominos. Silver bay horses will have mid to light bay bodies with lightened manes and tails and legs with minimal dark markings. Silver bays can be easily mistaken for chestnut horses. 

  
  

  The silver gene is also responsible for Equine Multiple Congenital Ocular Anomalies (MCOA). This condition causes a wide range of eye anomalies. Heterozygous silver horses have a less severe version while homozygous silver horses can have significant eye issues. Chestnut horses, which can not visibly show the silver gene, are still impacted by MCOA. [2]

  
  

  Silver horses on HorseGeneticGame.com have no negative impact from the silver gene.

• Citations:

  1. Brunberg, E., Andersson, L., Cothran, G., Sandberg, K., Mikko, S., & Lindgren, G. (2006). A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genetics, 7(46). https://pubmed.ncbi.nlm.nih.gov/17029645/ 
  2. Andersson, L. S., Wilbe, M., Viluma, A., Cothran, G., Ekesten, B., Ewart, S., & Lindgren, G. (2013). Equine Multiple Congenital Ocular Anomalies and Silver Coat Colour Result from the Pleiotropic Effects of Mutant PMEL. PLoS ONE, 8(9). https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0075639

• Examples:

  Silver Black E/? a/a Z/?, Silver Brown E/? A/? Z/?, Silver Bay E/? A/? Z/?

  

  
  

Champagne (SLC36A1)

• Last updated: 2026-01-19

  Common Names: Champagne

  Scientific Name: solute carrier family 36 (proton/amino acid symporter), member 1 (SLC36A1)

  Equine Chromosome:  14

  General Overview:

  The champagne gene evenly dilutes black pigment to a grayish brown and red to a peachy gold tone. The skin of champagne horses is pinkish to lavender with speckling, particularly on the nose, eyes, and genitals. Eyes are often amber to greenish in color. [1]
  
  Chestnut horses become a peachy golden color called gold champagne. They often have flaxen manes and tails, and can be easily mistaken for palomino. [2]
  
  Bay horses with champagne are called amber champagne. They end up a bronzy orange tone with slightly darker points. Manes and tails are darker than the body but can have heavy light color “frosting” and an overall orange tone. [2]

  
  

  Particularly dark bays and brown horses with champagne are called sable champagne. They have an overall mousy gray brown color with darker points. [2]
  
  Black horses become classic champagne. They can appear similar to sable champagnes with a mousy gray brown color and frequently darker points. [2]

• Citations:

  1. Cook D, Brooks S, Bellone R, Bailey E. Missense mutation in exon 2 of SLC36A1 responsible for champagne dilution in horses. PLoS Genet. 2008 Sep 19;4(9):e1000195. doi: 10.1371/journal.pgen.1000195. PMID: 18802473; PMCID: PMC2535566. https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000195 
  2. “Basic Champagne Colors.” Ichregistry.com, 2019, www.ichregistry.com/colors.htm  Accessed 19 Jan. 2026.

• Examples:

  Classic Champagne E/? a/a Ch/?, Sable Champagne E/? A/? Z/?

  

  
  

  Amber Champagne E/? A/? Ch/?, Gold Champagne e/e Ch/

  

  
  

Roan/Tobiano/Sabino/White Spotting (KIT)

• Last updated: 2026-01-23

  Common Names: KIT, Tobiano, Roan, White Spotting, Sabino, Dominant White

  Scientific Name: tyrosine-protein kinase KIT (KIT)

  Equine Chromosome: 3

  General Overview:

  Of all the genes associated with color in horses none is more dynamic and with more known alleles than KIT. A staggering 40+ forms have been discovered and it is expected many more are still to be found.

  
  

  Kit mutations cause standard looking white markings on the feet and face in more minimal forms, and large lacey broken markings that stretch up into the body in louder forms. Some forms of KIT result in completely white horses. Roaning, speckles and ticking are very common. Rarely horses with KIT mutations will present with blue eyes but it is still unclear if this is the result of KIT mutations or other white markings. 

  
  

  Some studies have also found that e/e horses can present with louder KIT markings than black and bay horses.  [21]

• Sabino vs. Dominant White vs. White Spotting

  Before KIT gene testing was possible, many white markings that shared a similar lacey edged texture were given the name sabino. This helped distinguish them from other known white spotting patterns like tobiano and frame. The first KIT mutation to be documented was sabino 1 in 2005. [6]

  
  

  Then in 2007 four new KIT mutations were located and named dominant white 1 through 4 as they appeared to be completely dominant and homozygous lethal.[7] This follows naming conventions for other similar genes from other species. It was assumed that the term sabino would be applied to non-homozygous lethal variants while the term dominant white would be used for the homozygous lethal variants.

  
  

  This assumption was upended in 2009 when seven new mutations were all documented in a single paper, all of which were added to the Dominant White series.[8] Since that time, all future sabino and max white style KIT mutations have been added to the W number sequence. When it became clear that not all of these mutations were in fact dominant or homozygous lethal some geneticists chose to start referring to them as white spotting.

  
  

  Technically only horses with sabino 1 should be called sabino, but the term sabino is widely used by horse people and many choose to continue to use the term. Alternatively, some use sabino-like to describe markings that are similar to the sabino 1 in appearance but do not test as sabino. Technically the term dominant white should be used for any KIT mutation that is fully or nearly fully white when heterozygous and lethal when homozygous.  White spotting should be used for KIT mutations that are not homozygous lethal. The problem is often it can be really unclear what category a mutation falls into.

  
  

  All four terms, sabino, sabino-like, dominant white, and white spotting, are ok to use in most situations. It is a good idea to know what each term means and to use the most correct one you are able to. It’s not however something to overly stress about and even the genetic labs don’t always use the terms consistently.

  
  

  HorseGeneticsGame.com uses sabino and white spotting for color naming.

• Specific Alleles:

  Tobiano - Tobiano is not actually a mutation of KIT but is instead an inversion in part of the regulatory area for KIT. Tobiano horses have large rounded patches of color on a white background. [1] Tobiano horses tend to have dark colored heads, chests, and flanks. Homozygous tobianos may be more prone to clusters of smaller spots called cat tracks or paw prints. 

  
  

  Roan 1,2,3 - Roan causes the body of the horse to have evenly dispersed white hairs, while the head, legs, mane, and tail are all left self colored. There are three currently known variants of roan. Roan 1 (R1), roan 2 (R2), and roan 3 (R3) all require one copy to show, and can be safely combined with each other. [2,3,4]

  
  

  Roan 1 is found in a large number of breeds including those found in Europe, and North and South America. [3]

  
  

  Roan 2 is limited to North American stock horse breeds. Famous sires with this variant include Metallic Cat and Peptoboonsmal.[3]

  
  

  Roan 3 is found primarily in quarter horses. Famous sires with this variant include Zippos Mr Good Bar, VS Code Blue, and VS Code Red.[4]

  
  

  There is a chance, because of the way gene testing works, that all 3 known roan types are actually the same functional mutation with different markers. [3,4]

  
  

  HorseGenticsGame.com currently only uses R to represent all 3 known roan variants. 

  
  

  Sabino1 - Sabino1 (SB1) is found in a wide number of breeds and is when heterozygous creates moderate to loud white markings that are lacey edged and roany in texture. Homozygous sabino horses have expensive white markings covering 90% or more of the horse. [6]

  
  

• White 1 - Found in Franches-Montagnes that descend from the stallion Cigale, this variant results in mostly white horses and is homozygous lethal.  [7]

  
  

  White 2 - Found in Thoroughbreds that descend from the stallion Kentucky Colonel, this variant results in mostly white horses and is homozygous lethal.  [7] 

  
  

  White 3 - Found in Arabians that descend from the stallion R Khasper, this variant results in mostly white horses and is homozygous lethal.  [7] 

  
  

  White 4 - Found in Camarillo White Horse that descend from the stallion Sultan, this variant results in mostly white horses and is homozygous lethal.  [7] 

  
  

  White 5 - Found in Thoroughbreds that descend from the stallion Puchilingui. Horses with W5 are roughly 40% to 60% white. It can combine with minimal KIT mutations like w20 to produce all white individuals. It is presumed to be homozygous lethal with itself and other mutations of KIT that are also homozygous lethal. [8] 

  
  

  White 6 -  Found only in the Thoroughbred mare Marumatsu Live. She never produced any foals and the W6 variant passed with her. She was mostly white with heavy chestnut speckles over the majority of her body. [8]

  
  

  White 7 -  Found in Thoroughbreds that descend from the mare Turf Club. W7 horses are 60 to 90% white, with color along the top line and extensive speckles of color over the body. Some all white W7 horses are also known but it is unclear if they have an additional KIT mutation. W7 is suspected to be homozygous lethal. [8]

  
  

  White 8 - Found in Icelandic horses that descend from Þokkadís vom Rosenhof. W8 horses tend to have 20 to 40% white often with heavy lacing, ticking, and colored speckles. It can produce all white horses when combined with other white mutations. It is probably not homozygous lethal. [8]

  
  

  White 9- W9 is found in a single line of Holstein horses. [8] 

  
  

  White 10 - Found in Quarter and Paint horses that descended from GQ Santana. W10 horses have 90% plus white coverage with very limited speckling on the body hair. W10 is homozygous lethal.  [8]

  
  

  White 11 - Found in a single line South German Draft horses. [8] 

  
  

  White 12 - Found in a single Thoroughbred which is now deceased. The foal died at 5 weeks with possible complications from his KIT mutation. This variant is extinct. [9]

  
  

  White 13 -  Found in Quarter Horses and Miniature Horse breeds. Heterozygous horses are completely white, and are homozygous lethal.[10]

  
  

  White 14 - Found in Thoroughbreds that descend from the mare Shirayukihime. Heterozygous horses are all white, or mostly white with moderately sized lacey patches of color over the body.  [10] 

  
  

  White 15 - Found in Arabians that descend from the stallion Khartoon Khlassic. Heterozygous individuals tend to have white faces and legs, and white spots on the neck underside and belly. Homozygous individuals tend to be entirely white. [10]

  
  

  White 16 - Found in Oldenburgs that descend from the mare Celine. Horses with one copy are 30%+ white, with white legs and face, and many markings through the entire body. Many individuals are also completely white, and it is unclear if they are interacting with other KIT mutations or not. The lethality of this mutation is unclear. [10] 

  
  

  White 17 - Found in a single all white Japanese Draft horse. [10]

  
  

  White 18 - Found in warmbloods that descend from the Swiss mare Colorina Von Hoff. She was approximately 60% white with heavy speckling. It is unclear if she ever had offspring. [11]

  
  

  White 19 -  Found in Arabian horses that descend from the mare Fantasia Vu. Heterozygous horses have 4 white legs, moderate face markings, and frequent lacey belly spotting. They are 20 to 50% white.  Homozygous horses are completely white and may have associated health problems. [11]

  
  

  White 20 - Found in most breeds and is the most common of all KIT mutations. W20 horses can range from no white at all to around 20% white, and homozygous individuals may be visually indistinguishable from heterozygous individuals. Some W20 horses have belly spots, which can be more common when homozygous.  W20 has a boosting effect and can make other KIT mutations significantly louder. [11]

  
  

  White 21 - Found in Icelandic horses that descend from the stallion Ellert frá Baldurshaga. W21 causes extensive roaning throughout the body. [12]

  
  

  White 22 - Found in Thoroughbreds that descend from the mare Not Quite White. Horses with one copy range from 20 to 40% white, with heavy roaning. Can produce completely white horses when paired with w20 and other minimal white KIT mutations. Appears to be lethal when homozygous. [13]

  
  

  White 23 -  Found in Arabians that descend from the stallion Boomori Simply Stunning. W23 horses are all white. This mutation is thought to be extinct. [14]

  
  

  White 24 - Found in Italian Trotters the descended from the stallion Via Lattea. Results in completely white individuals when heterozygous.  [15]

  
  

  White 25 - Found in Australian Thoroughbreds that descend from the mare Laughyoumay. Results in near or completely white individuals when heterozygous.  [16]

  
  

  White 26 -  Found in Australian Thoroughbreds that descend from the mare Marbrowell. Produces partially white coats with heavy roaning when heterozygous. [16]

  
  

• White 27 - Found in Australian Thoroughbreds that descend from the mare Milady Fair. Produce extensive speckles on an white background. [16]

  
  

  White 28 - Found in a single German Riding Pony. [17]

  
  

  White 29  - N/A skipped number. 

  
  

  White 30 - Found in Berber horses that descend from the stallion Aghilasse. Produces an all white coat when heterozygous.[18]

  
  

  White 31 - Found in Quarter Horses that descend from the stallion Cookin Merada. Produces face, leg, belly and body markings with highly irregular edges.  [19]

  
  

  White 32 - Found in Quarter Horses and Paints that descend from the mare Small Town Scandal. Produces face legs and belly white when heterozygous.Homozygous horses are 90% plus white with extensive roany speckles. [19]

  
  

  White 33 - Found in a single Standardbred mare.  [20]

  
  

  White 34 - Found in a large number of breeds. Causes large blazes, socks and belly spots when heterozygous. [21]

  
  

  White 35 - Found in the “A Sudden Holiday” family of quarter horses. Causes minimal white markings. [22]

  
  

  White 36 - N/A skipped number. 

  
  

  White 37 -  Found in Anglo-Arabian horses the descend from the stallion Viconte des Neigas. [23]

  
  

  White 38 - Found in Polish Sport horses the descend from the mare Greenlough Melody G. [23]

  
  

  White 39 - Found in a stock type mare named Oakbank Pretty as a Penny with extensive full body roaning and 95%+ white.  [23]

• HorseGeneticGame.com Specific Mutations

  Donkey Dominant White (DDW)- is a real allele of KIT found in domestic donkeys. [24] It causes completely white individuals when heterozygous and is lethal with all other KIT mutations including roan.  

  
  

  Powder White (PW) - Is an imaginary allele created for HorseGeneticsGame.com. It adds roaning from the top down on a horse, like powdered snow, and is not lethal when combined with any other KIT mutations. 

  
  

  Manchado (M) - Is a spotting pattern found in South America and Argentina especially. It produces dramatic full body speckles and patches throughout the entire body. The current cause is unknown. In HorseGeneticsGame.com this color is represented by KITM. It is dominant in game but probably recessive in real life.

  
  

• Horses with more than 2 KIT alleles

  A frequent point of confusion I see involves horses testing positive for more than two kit alleles (mutations). Of course each horse only has two copies of KIT, one on each copy of chromosome 3, but KIT is a very large gene. KIT itself is approximately 82 kilobases long [7] with its various mutations distributed across not only the entire length of the gene but also spanning into its regulatory regions as well. [1]

  
  

  Some mutations of KIT have occurred on top of previously existing mutations, like W22 which is a mutation that happened on the previously existing W20 allele. [26] That means all W22 horses will also test as having W20. [25] It’s two mutations occupying a single gene on a single chromosome. 

  
  

  Crossover events can also happen, where two previously distinct KIT mutations become linked on the same chromosome in some lines. This has been documented with compound W32SB1, W32W20, W32W35, W34W35 and even W19W34W35 variants.[25]

  
  

  HorseGeneticsGame.com does not currently have compound KIT alleles.

• Lethality:

  What follows is what I have come to understand from reading a large number of papers on KIT and its mechanics. I do not know of any study that lays this information out directly.

  
  

  Mutations become lethal when a critical to life developmental process no longer works. KIT performs an important action in the body. Like with a car, a lot of things can break and the car can keep running. At some point though, just too many systems have failed and the engine will no longer start. There are no clean cut rules about KIT lethality. Less white means less parts of the process are broken. More white means more of it is broken and it’s more likely that the combination is lethal. 

  
  

  KIT mutations range widely in just how broken they are. White 35 causes extremely minimal white markings on its own and boosts the expression of other KIT mutations. It is probably lethal when combined with the max white KIT mutations and probably not lethal with moderate white causing mutations.. Mutations that produce all white individuals with only a single copy are definitely going to be lethal with other high white KIT mutations and might also be lethal with roan, or even tobiano. 

  
  

  The more white produced by an allele of KIT the more likely it is to be lethal when homozygous or when combined with other KIT mutations. Two loud KIT alleles are more likely to be lethal than two more minimal KIT alleles. As KIT has incomplete dominance a specific combination may be lethal in some cases but not others.

• Citations:

  1. Brooks SA, Lear TL, Adelson DL, Bailey E. A chromosome inversion near the KIT gene and the Tobiano spotting pattern in horses. Cytogenet Genome Res. 2007;119(3-4):225-30. doi: 10.1159/000112065. Epub 2008 Feb 1. PMID: 18253033. https://pubmed.ncbi.nlm.nih.gov/18253033/ 
  2. Voß, K.; Tetens, J.; Thaller, G.; Becker, D. Coat Color Roan Shows Association with KIT Variants and No Evidence of Lethality in Icelandic Horses. Genes 2020, 11, 680. https://doi.org/10.3390/genes11060680 
  3.  Everts, R.E.; Caron, R.; Foster, G.; McLoone, K.; Martin, K.; Brooks, S.A.; Lafayette, C. Identification of Two Genetic Haplotypes Associated with the Roan Coat Color in the American Quarter Horse and Other Equine Breeds. Animals 2025, 15, 1705. https://doi.org/10.3390/ani15121705
  4. Everts, R.E.; Caron, R.; Foster, G.; McLoone, K.; Simiele, L.; Martin, K.; Brooks, S.A.; Lafayette, C. Identification of a Novel Haplotype Associated with Roan Coat Color in American Quarter Horses. Animals 2025, 15, 2386.
  5. https://www.preprints.org/manuscript/202506.2208?fsuid=%2317HZ9P%23b2eda092-7826-4044-89bd-8f15377678b7:9d9546d3-de99-4707-aee6-fc4330ab9959:1768821949850::1%23/1797312171
  6. Brooks SA, Bailey E. Exon skipping in the KIT gene causes a Sabino spotting pattern in horses. Mamm Genome. 2005 Nov;16(11):893-902. doi: 10.1007/s00335-005-2472-y. Epub 2005 Nov 11. PMID: 16284805. https://pubmed.ncbi.nlm.nih.gov/16284805/ 
  7.  Haase B, Brooks SA, Schlumbaum A, Azor PJ, Bailey E, Alaeddine F, et al. (2007) Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses. PLoS Genet 3(11): e195. https://doi.org/10.1371/journal.pgen.0030195 
  8. Haase B, Brooks SA, Tozaki T, Burger D, Poncet PA, Rieder S, Hasegawa T, Penedo C, Leeb T. Seven novel KIT mutations in horses with white coat colour phenotypes. Anim Genet. 2009 Oct;40(5):623-9. doi: 10.1111/j.1365-2052.2009.01893.x. Epub 2009 May 6. PMID: 19456317. https://pubmed.ncbi.nlm.nih.gov/19456317/ 
  9. Holl H et al., “De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern.” (2010) Anim Genet. 41: 196-8.  https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2052.2010.02135.x 
  10. Haase B et al., “Five novel KIT mutations in horses with white coat colour phenotypes.” (2011) Anim Genet. 42: 337-9. https://www.researchgate.net/publication/51109575_Five_novel_KIT_mutations_in_horses_with_white_coat_colour_phenotypes 
  11. Hauswirth R, Jude R, Haase B, Bellone RR, Archer S, Holl H, Brooks SA, Tozaki T, Penedo MC, Rieder S, Leeb T. Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes. Anim Genet. 2013 Dec;44(6):763-5. doi: 10.1111/age.12057. Epub 2013 May 9. PMID: 23659293.  https://www.researchgate.net/figure/Coat-colour-phenotypes-of-horses-with-different-genotypes-a-Appaloosa-horse-carrying_fig1_236673503 
  12.  Haase B, Jagannathan V, Rieder S, Leeb T. A novel KIT variant in an Icelandic horse with white-spotted coat colour. Anim Genet. 2015 Aug;46(4):466. doi: 10.1111/age.12313. Epub 2015 Jun 9. PMID: 26059442.  https://www.researchgate.net/publication/278045151_A_novel_KIT_variant_in_an_Icelandic_horse_with_white-spotted_coat_colour 
  13.  Dürig N, Jude R, Holl H, Brooks SA, Lafayette C, Jagannathan V, Leeb T. Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes. Anim Genet. 2017 Aug;48(4):483-485. doi: 10.1111/age.12556. Epub 2017 Apr 26. PMID: 28444912. https://pubmed.ncbi.nlm.nih.gov/28444912/ 
  14.  Holl H.M., Brooks S.A., Carpenter M.L., Bustamante C.D., Lafayette C. A novel splice mutation within equine KIT and the W15 allele in the homozygous state lead to all white coat color phenotypes. Anim. Genet. 2017;48:497–498. doi: 10.1111/age.12554. https://pubmed.ncbi.nlm.nih.gov/28378922/ 
  15. Capomaccio S., Milanesi M., Nocelli C., Giontella A., Verini-Supplizi A., Branca M., Silvestrelli M., Cappelli K. Splicing site disruption in the KIT gene as strong candidate for white dominant phenotype in an Italian Trotter. Anim. Genet. 2017;48:727–728. doi: 10.1111/age.12590.  https://pubmed.ncbi.nlm.nih.gov/28856698/ 
• 16. Hoban R., Castle K., Hamilton N., Haase B. Novel KIT variants for dominant white in the Australian horse population. Anim. Genet. 2018;49:99–100. doi: 10.1111/age.12627. 
  17. Hug P., Jude R., Henkel J., Jagannathan V., Leeb T. A novel KIT deletion variant in a German Riding Pony with white-spotting coat colour phenotype. Anim. Genet. 2019;50:761–763. doi: 10.1111/age.12840. 
  18. Martin K., Patterson Rosa L., Vierra M., Foster G., Brooks S.A., Lafayette C. De novo mutation of KIT causes extensive coat white patterning in a family of Berber horses. Anim. Genet. 2021;52:135–137. doi: 10.1111/age.13017.
  19. Patterson Rosa L., Martin K., Vierra M., Foster G., Lundquist E., Brooks S.A., Lafayette C. Two Variants of KIT Causing White Patterning in Stock-Type Horses. J. Hered. 2021;112:447–451. doi: 10.1093/jhered/esab033.
  20. Esdaile E., Till B., Kallenberg A., Fremeux M., Bickel L., Bellone R.R. A de novo missense mutation in KIT is responsible for dominant white spotting phenotype in a Standardbred horse. Anim. Genet. 2022;53:534–537. doi: 10.1111/age.13222. https://onlinelibrary.wiley.com/doi/abs/10.1111/age.13222 
  21. Patterson Rosa L., Martin K., Vierra M., Lundquist E., Foster G., Brooks S.A., Lafayette C. A KIT Variant Associated with Increased White Spotting Epistatic to MC1R Genotype in Horses (Equus caballus) Animals. 2022;12:1958. doi: 10.3390/ani12151958. https://www.mdpi.com/2076-2615/12/15/1958 
  22. McFadden A., Martin K., Foster G., Vierra M., Lundquist E.W., Everts R.E., Martin E., Volz E., McLoone K., Brooks S.A., et al. 5′UTR Variant in KIT Associated With White Spotting in Horses. J. Equine Vet. Sci. 2023;127:104563. doi: 10.1016/j.jevs.2023.104563. 
  23. Obradovic NA, McFadden A, Martin K, Vierra M, McLoone K, Martin E, Thomas A, Everts RE, Brooks SA, Lafayette C. "Three Novel KIT Polymorphisms Found in Horses with White Coat Color Phenotypes." (2025) Animals. 15(7), 915; 15(7), 915. https://www.mdpi.com/2076-2615/15/7/915. 
  24. Haase, B., Rieder, S., & Leeb, T. (2015). Two variants in the KIT gene as candidate causative mutations for a dominant white and a white spotting phenotype in the donkey. Animal Genetics, 46(3), 321-324. doi: 10.1111/age.12282 
  25. McFadden, A.; Vierra, M.; Robilliard, H.; Martin, K.; Brooks, S.A.; Everts, R.E.; Lafayette, C. Population Analysis Identifies 15 Multi-Variant Dominant White Haplotypes in Horses. Animals 2024, 14, 517. https://doi.org/10.3390/ani14030517 
  26. W22 Dürig, N.; Jude, R.; Holl, H.; Brooks, S.A.; Lafayette, C.; Jagannathan, V.; Leeb, T. Whole genome sequencing reveals a novel deletion variant in the KIT gene in horses with white spotted coat colour phenotypes. Anim. Genet. 2017, 48, 483–485. 

Splash White (MITF/PAX3)

• Last updated: 2026-01-20

  Common Names: Splash, or Splash White: 1/2/3/4/5/6/7/8/9/10 and M

  Scientific Name: Microphthalmia-associated transcription factor (MITF) and Paired box 3 (PAX3)

  Equine Chromosome: MITF on 16, PAX3 on 6

  General Overview:

  There are currently 11 documented variations of splash. Splash 1,3,5,6,7,8,9 and M are located on MITF. Splash 2, 4 and 10 are located on PAX3. [1,2,3,4,5,6,7,8] The MITF and PAX3 variants are similar enough in behavior that they are both treated as a single phenotype called splash white.

  
  

  Splash mutations result in face markings that range from blazes to fully bald faces. They often have one or more blue eyes. Splash white horses normally have high white leg markings on 3 or more legs. Minimal expressions of splash may be indistinguishable from other common markings. When homozygous, splash white horses have extensive white markings, normally covering the entirety of the legs and face, often including the belly, and sometimes resulting in completely white horses.

  
  

  Splash white markings are frequently linked to deafness. Larger white markings, particularly those that cover the ears are the most likely to result in deaf individuals. [1] 

  
  

  Currently only splash white 1, 3, and M are found in HorseGeneticsGame.com.

• Specific Alleles:
  Splash 1 is located on MITF and has been found in a white variety of breeds including stock horses, warmbloods, icelandics, miniatures and more.

  
  

  Splash 2 is located on PAX3 and was documented in 2012 in several lines of Quarter and Paint horses. [1] This mutation was originally thought to be homozygous lethal, but is now known to be viable. Homozygous individuals are normally deaf. [3] My personal conjecture is that this mutation is probably sometimes embryonic lethal and sometimes not depending on other developmental factors. Splash 2 is currently homozygous lethal in HorseGeneticsGame.com

  
  

  Splash M is located on MITF. It was found in a single Franches-Montagnes horse who has since been gelded. He appeared to have a de novo mutation, with neither of his parents sharing the same allele. [1] Since there are no other splash M horses and never will be another this form was not given a number in the sequence. It is instead known as splash M or macchiato. In HorseGeneticsGame.com splash M horses have a diluted body color with large leg and face markings with laced edges. They can potentially have blue eyes. 

  
  

  Splash 3 horses descend from the AQHA stallion TD Kid. It results in large white markings when heterozygous and is probably homozygous lethal. [1]

  
  

  Splash 4 is a rare PAX3 mutation found in the Iza Last Jet line of appaloosa horses. It causes large blazes and partially blue eyes. It is potentially homozygous lethal. [2]

  
  

  Splash 5, 6 and 7 are mutations of MITF found in quarter horses and paint horses. They produce large amounts of leg markings, face white, blue eyes and frequent deaf individuals when heterozygous. All are presumed homozygous lethal with themselves and with other loud MITF mutations. [4,5,6]

  
  

  Splash 8 is a mutation of MITF found in a single family of thoroughbreds. This variant produces moderate bald faces, leg white and blue eyes. Some are known to be deaf. Its lethality when homozygous is unknown. [7]

  
  

  Splash 9 is an MITF mutation found in Pura Raza Española horses. It results in moderate bold faces, leg white and blue eyes. Deafness has not been found in splash 9 horses so far. Its lethality when homozygous is unknown.[8]

  
  

  Splash 10 is a PAX3 mutation found in Pura Raza Española horses.It results in moderate bold faces, leg white and blue eyes. Deafness has not been found in splash 10 horses so far. Its lethality when homozygous is unknown.[8]

  
  

• Lethality:

  What follows is what I have come to understand from reading a large number of papers on splash white and its mechanics. I do not know of any study that lays this information out directly.

  
  

  Mutations become lethal when a critical to life developmental process no longer works. MITF and PAX3 both perform important actions in the body. Like with a car, a lot of things can break and the car can keep running. At some point though, just too many systems have failed and the engine will no longer start. There are no clean cut rules about splash white lethality. Less white means less parts of the process are broken. More white means more of it is broken and it’s more likely that the combination is lethal.

  
  

  The more white produced by an allele of splash the more likely it is to be lethal when homozygous or when combined with other splash mutations. Two loud splash alleles are more likely to be lethal than two more minimal splash alleles. As splash has incomplete dominance a specific combination may be lethal in some cases but not others. Combining an MITF mutation with a PAX3 mutation is less lethal than combining two MITF or two PAX3 mutations.

• Citations:

  1. Hauswirth R, Haase B, Blatter M, Brooks SA, Burger D, Drögemüller C, Gerber V, Henke D, Janda J, Jude R, Magdesian KG, Matthews JM, Poncet PA, Svansson V, Tozaki T, Wilkinson-White L, Penedo MC, Rieder S, Leeb T. Mutations in MITF and PAX3 cause "splashed white" and other white spotting phenotypes in horses. PLoS Genet. 2012;8(4):e1002653. doi: 10.1371/journal.pgen.1002653. Epub 2012 Apr 12. Erratum in: PLoS Genet. 2019 Aug 2;15(8):e1008321. doi: 10.1371/journal.pgen.1008321. PMID: 22511888; PMCID: PMC3325211. https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002653 
  2. Hauswirth R, Jude R, Haase B, Bellone RR, Archer S, Holl H, Brooks SA, Tozaki T, Penedo MC, Rieder S, Leeb T. Novel variants in the KIT and PAX3 genes in horses with white-spotted coat colour phenotypes. Anim Genet. 2013 Dec;44(6):763-5. doi: 10.1111/age.12057. Epub 2013 May 9. PMID: 23659293.https://www.researchgate.net/publication/236673503_Novel_variants_in_the_KIT_and_PAX3_genes_in_horses_with_white-spotted_coat_colour_phenotypes 
  3. Avila, F., Hughes, S.S., Magdesian, K.G., Penedo, M.C.T, and Bellone, R.R. 2022. Breed Distribution and Allele Frequencies of Base Coat Color, Dilution, and White Patterning Variants across 28 Horse Breeds. Genes 13(9):1641. https://www.researchgate.net/publication/363564721_Breed_Distribution_and_A
  4. Henkel J, Lafayette C, Brooks SA, Martin K, Patterson-Rosa L, Cook D, Jagannathan V, Leeb T. Whole-genome sequencing reveals a large deletion in the MITF gene in horses with white spotted coat colour and increased risk of deafness. Anim Genet. 2019 Apr;50(2):172-174. doi: 10.1111/age.12762. Epub 2019 Jan 15. PMID: 30644113. https://www.semanticscholar.org/paper/Whole-genome-sequencing-reveals-a-large-deletion-in-Henkel-Lafayette/092bc279d1aa976992fbc3c708a675efc5997533 
  5. Magdesian KG, Tanaka J, Bellone RR. A De Novo MITF Deletion Explains a Novel Splashed White Phenotype in an American Paint Horse. J Hered. 2020 May 20;111(3):287-293. doi: 10.1093/jhered/esaa009. PMID: 32242630; PMCID: PMC7238438. https://pubmed.ncbi.nlm.nih.gov/32242630/ 
  6. Patterson Rosa, L., Martin, K., Vierra, M., Foster, G., Brooks, S. A., & Lafayette, C. (2022). Non-frameshift deletion on MITF is associated with a novel splashed white spotting pattern in horses (Equus caballus). Animal Genetics, 53(4), 538–540. doi: 10.1111/age.13225
  7.  Bellone RR, Tanaka J, Esdaile E, Sutton RB, Payette F, Leduc L, Till BJ, Abdel-Ghaffar AK, Hammond M, Magdesian KG. A de novo 2.3 kb structural variant in MITF explains a novel splashed white phenotype in a Thoroughbred family. Anim Genet. 2023 Dec;54(6):752-762. doi: 10.1111/age.13352. Epub 2023 Sep 12. PMID: 37697831. https://onlinelibrary.wiley.com/doi/full/10.1111/age.13352 
  8. McFadden A, Martin K, Foster G, Vierra M, Lundquist EW, Everts RE, Martin E, Volz E, McLoone K, Brooks SA, Lafayette C. Two Novel Variants in MITF and PAX3 Associated With Splashed White Phenotypes in Horses. J Equine Vet Sci. 2023 Sep;128:104875. doi: 10.1016/j.jevs.2023.104875. Epub 2023 Jul 3. PMID: 37406837. https://www.researchgate.net/publication/372087978_Two_Novel_Variants_in_MITF_and_PAX3_Associated_with_Splashed_White_Phenotypes_in_Horses 

• Examples:

  A range of splash expressions

  

  
  

Leopard Complex (TRPM1/ECA3P)

• Last updated: 2026-01-21

  About LP:

  Common Names: Leopard, Leopard Complex, Appaloosa, Spotted, tiger 

  Scientific Name: Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1)

  Equine Chromosome: 1

  
  

  About PATN1:

  Common Names: Pattern 1, Blanket

  Scientific Name: RING finger and WD repeat domain 3 (RFWD3)

  Equine Chromosome: 3

  
  

  General Overview:

  Leopard spotting is the general term for a roany polka dot marking pattern in horses, primarily known from the Appaloosa breed but also found in breeds like the Knabstrupper, Noriker and Miniature horses. Its expression is turned on or off by the LP allele of TRPM1. Horses with the LP allele get progressively whiter with age, with boney areas on the face and joints turning white last.[1]
  
  The PATN1 mutation of RFWD3 modifies the expression of LP. Horses with a single copy of PATN1 tend to have a blanket of white, ranging from a small area over the hips, to a large blanket over all of the hips, back and shoulders. Horses with two copies tend to have very large blankets or even be entirely covered in white. [2] PATN1 is the major factor controlling blanket size but does not fully explain all blanket size variation in LP horses. Many other undocumented factors seem to also impact blanket size. 

  
  

  Horses with one copy of LP and a blanket will show polka dots of the base color clustered in and around that blanket. Horses with two copies of LP will have the blanket but few to no polka dots.

• Expression:

  All LP horses will have “LP characteristics” which include mottled skin, stripped hooves, and a viable white sclera, but not all LP horses display varnishing, a blanket, or spots. These characteristic only horses are sometimes called “solid” or "carrier" horses.

  
  

  Varnish: A horse with LP characteristics and white hairs throughout the body that increase with age.  Varnish horses can be distinguished from true roans because varnish avoids boney areas like joints and prominent facial bones, white true roan is even over the entire body but absent from the head, legs, mane and tail. An LP horse may be “varnish” in conjunction with any blanket size. For example a “varnish snowcap”.

  
  

  Lacey Blanket: A very small lacey pattern of white over the hips. It may be very difficult to detect heterozygous LP spotting on these horses.

  
  

  Spotted Blanket: A wash of completely white hair over pink skin that originates from the top of the hips and can cover just the hind quarters or be as large as the entire hips, torso and shoulder area. The blanket is accented throughout by polka dots. These horses are heterozygous for LP.

  
  

  Snowcap Blanket: Like a spotted blanket but lacks the polka dots. If present at all, they are very small and infrequent. These horses are homozygous for LP. 

  
  

  Near Leopard: A horse with a very extensive blanket that extends into the neck and legs, accented by polka dots. These horses are heterozygous for LP.

  
  

  Near Fewspot: Same as a near leopard but lacks the polka dots. If present at all they are very small and infrequent. These horses are homozygous for LP.

  
  

  Leopard: A horse whose entire body is covered in blanket marking, giving them the appearance of an all white horse with polka dots of color. These horses do not tend to show visible varnishing with age. These horses are heterozygous for LP.
  
  Fewspot: Same as a leopard but lacks the polka dots. If present at all they are very small and infrequent. These horses are homozygous for LP. 

• Night Blindless:

  The LP gene has been found to be the direct cause of congenital stationary night blindness (CSNB). All LP/LP lack the ability to see at night so extra consideration should be given to their environment to prevent night time injury. Horses with only one copy of LP do not seem to be impacted. [1] There is no evidence blanket size impacts CSNB status. LP/LP horses have no negative health impacts in HorseGeneticsGame.com

• Citations:

  1. Bellone RR, Brooks SA, Sandmeyer L, Murphy BA, Forsyth G, Archer S, Bailey E, Grahn B. Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus). Genetics. 2008 Aug;179(4):1861-70. doi: 10.1534/genetics.108.088807. Epub 2008 Jul 27. PMID: 18660533; PMCID: PMC2516064.  https://www.researchgate.net/publication/51431473...s 
  2. Holl HM, Brooks SA, Archer S, Brown K, Malvick J, Penedo MC, Bellone RR. Variant in the RFWD3 gene associated with PATN1, a modifier of leopard complex spotting. Anim Genet. 2016 Feb;47(1):91-101. doi: 10.1111/age.12375. Epub 2015 Nov 16. PMID: 26568529. https://pubmed.ncbi.nlm.nih.gov/26568529/ 

• Examples:

  Characteristic/Solid, Varnish, Lace Blanket

  

  
  

  Spotted Blanket LP/lp, Snowcap Blanket LP/LP

  

  
  

  Near Leopard LP/lp, Near Fewspot LP/LP

  

  
  

  Leopard LP/lp, Fewspot LP/LP

  

  
  

Frame (EDNRB)

• Last updated: 2026-01-19

  Common Names: Frame, Overo, Lethal White Overo

  Scientific Name: Endothelin Receptor Type B (EDNRB)

  Equine Chromosome: 17

  General Overview:

  The frame gene is named for the frame of color it tends to leave around a white torso. It readily combines with other pinto markings like splash and tobiano to produce particularly bold markings. Frame is incompletely dominant requiring only one copy to show. When homozygous it produces all or nearly all white foals who do not live more than a few days. [1]

• Citations:
  Santschi EM, Purdy AK, Valberg SJ, Vrotsos PD, Kaese H, Mickelson JR. Endothelin receptor B polymorphism associated with lethal white foal syndrome in horses. Mamm Genome. 1998 Apr;9(4):306-9. doi: 10.1007/s003359900754. PMID: 9530628.  https://pubmed.ncbi.nlm.nih.gov/9530628/

• Examples:

  A range of frame expressions

  

  
  

Tiger Eye (SLC24A5)

• Last updated: 2026-01-19

  Common Names: Tiger Eye

  Scientific Name: Solute Carrier Family 24, Member 5 (SLC24A5)

  Equine Chromosome: 1

  General Overview:

  Tiger eye is found in the Puerto Rican Paso Fino breed of horse and causes lighter than normal eye coloration. Tiger eye lightens brown eyes to yellow, amber or even orange. There are two known alleles of tiger eye, TE1 and TE2. Tiger eye requires two copies. TE1/TE1, TE2/TE2, and TE1/TE2 all appear to be functionally the same.[1]

• Citations:

  1. Mack M, Kowalski E, Grahn R, Bras D, Penedo MCT, Bellone R. Two Variants in SLC24A5 Are Associated with "Tiger-Eye" Iris Pigmentation in Puerto Rican Paso Fino Horses. G3 (Bethesda). 2017 Aug 7;7(8):2799-2806. doi: 10.1534/g3.117.043786. PMID: 28655738; PMCID: PMC5555483. https://pubmed.ncbi.nlm.nih.gov/28655738/

• Examples:

  A bay horse with TE1/TE1

  

  
  

Height Regulation (HMGA2/LCORL)

• Last updated: 2026-01-20

  Common Names: Height Regulator

  Scientific Name: High-mobility group AT-hook 2 (HMGA2) and Ligand-Dependent Nuclear Receptor Corepressor-Like (LCORL)

  Equine Chromosome: HMGA2 on 6, LCORL on 3

  General Overview:

  So far two genes have been documented that control the majority of highest variation in horses. An allele of HMGA2 has been found in Shetland Ponies and results in reduced growth, with two copies causing more reduction than 1 copy.[1] An allele of LCORLis known to cause increased height with two copies causing more height gain than 1 copy. [2]
  
  Currently only HMGA2 is found in HorseGeneticsGame.com

• Citations:

  1. Frischknecht M, Jagannathan V, Plattet P, Neuditschko M, Signer-Hasler H, Bachmann I, Pacholewska A, Drögemüller C, Dietschi E, Flury C, Rieder S, Leeb T. A Non-Synonymous HMGA2 Variant Decreases Height in Shetland Ponies and Other Small Horses. PLoS One. 2015 Oct 16;10(10):e0140749. doi: 10.1371/journal.pone.0140749. PMID: 26474182; PMCID: PMC4608717. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0140749 
  2. Metzger J, Schrimpf R, Philipp U, Distl O. Expression levels of LCORL are associated with body size in horses. PLoS One. 2013;8(2):e56497. doi: 10.1371/journal.pone.0056497. Epub 2013 Feb 13. PMID: 23418579; PMCID: PMC3572084.https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0056497 

• Examples:

  HMGA2 -/- , HMGA2 A/- , HMGA2 A/A

  

  
  

Mushroom (MFSD12)

• Last updated: 2026-01-19

  Common Names: Mushroom

  Scientific Name: major facilitator superfamily domain containing 12 (MFSD12 )

  Equine Chromosome: 7

  General Overview:

  Mushroom is a dilution gene that impacts red pigment only and is found in Shetland Ponies. It is recessive and requires two copies to show. Mushroom horses have a sepia tone similar to a crimini mushroom with e/e individuals often having flaxen manes and tails. Bay horses can show a mild dilution in the brown areas of their coat. It has no known impact on black horses. [1]

• Citations:

  1. Tanaka J, Leeb T, Rushton J, Famula TR, Mack M, Jagannathan V, Flury C, Bachmann I, Eberth J, McDonnell SM, Penedo MCT, Bellone RR. Frameshift Variant in MFSD12 Explains the Mushroom Coat Color Dilution in Shetland Ponies. Genes (Basel). 2019 Oct 19;10(10):826. doi: 10.3390/genes10100826. PMID: 31635058; PMCID: PMC6827053.
     https://pubmed.ncbi.nlm.nih.gov/31635058/

• Examples:

  Chestnut e/e Mu/?, Chestnut Mushroom e/e mu/mu

  

  
  

  Bay e/e Mu/?, Bay Mushroom e/e mu/mu

  

  
  

Glossaries

Glossary of Colors

Glossary of Terms

• A

  • Albino - The complete absence of both eumelanin and pheomelanin. Many definitions include the presence of red eyes. There are no known albino genes in horses.

    Albino is a particularly complex term because its use varies depending on species and who is using the term. For example medical albinism in humans is defined as a reduction in pigment and does not require complete lack of pigment or red eyes.  The SLC45A2 responsible for cream in horses is also responsible for a type of human albinism. [1]  Breeders of reptiles will often use albino for color morphs that may not meet more stringent definitions for the term.[2]
    
    

    1. National Organization for Albinism and Hypopigmentation. “Information Bulletin – What Is Albinism?” National Organization for Albinism and Hypopigmentation, Feb. 2018, albinism.org/information-bulletin-what-is-albinism/.
    2. Animals, In. “Wisconsin Herpetological Association.” Wisconsin Herpetological Association, 11 Mar. 2019, www.wisconsinherps.org/educational-articles/blog-post-title-one-j9a6d. 

  • Allele - A specific variant of a gene. For example: The extension gene has two alleles black(E) and red(e).
• B
• C

  • Cell - An enclosed lipid membrane that contains the nucleus, where DNA is stored, and membrane-bound organelles. The place where proteins and polymers, like melanin, are produced.

  • Chromosome - A complete segment of DNA, containing many individual genes. Horses have 32 pairs of chromosomes.

  • Co-dominant - When two alleles of a gene are expressed at the same time resulting in both being displayed. For example: A horse with the tobiano allele of KIT and the roan allele of KIT will display both genes at the same time. Neither allele is dominant and the alleles do not blend to create a new third expression.
• D

  • Dilution - A gene that results in a reduction of pigment production. In horses champagne, cream (and its alleles), dun, and silver are the colors normally referred to as dilutions. Some individuals only use the term dilution when referring to the cream gene.

  • Dominant - When one allele of a gene masks the effect of another allele of that gene. For example the black(E) allele of extension is dominant over the red(e) allele.
• E

  • Embryonic - Referring to the the first few weeks of development after insemination.

  • Eumelanin - The dark form of melanin, responsible for black to brown shades. Present in horses with the Black(E) allele of the extension gene.
• F
• G

  • Gene - A heritable unit of DNA that controls protein production, development etc. of an individual.

  • Genotype - The specific combination of inherited genes that makes up an individual's DNA. As opposed to phenotype. For example: The genotype of a homozygous black and bay horse is E/E A/A.
• H

  • Hyperpigmentation - Higher than normal amount of pigment formation.

  • Hypopigmentation - Less than normal amount of pigment formation.
• I

  • Incomplete Dominance - When two alleles of the same gene are both expressed at the same time resulting in a new blended expression. For example: A chestnut horse is N/N for cream, and a cremello horse is Cr/Cr for cream. When bred together the produce a palomino horse that N/Cr for cream with a color that is in between the parents colors.
• J
• K

  • Keratinocyte - A cell that produces keratin, often in the form of skin, hair, and hooves. Melanin is primarily stored in these cells.
• L
• M

  • Melanin - A natural pigment produced in melanocytes and stored in keratinocytes. Horses produce two forms of melanin; eumelanin and pheomelanin.

  • Melanocyte - A type of cell which produces melanin.

  • Mutation - A change in the DNA sequence.
• N
• O
• P

  • Protein - A large complex molecule built from amino acids based on instructions provided by DNA. Many genes code for a protein.

  • Polymorphism - Having two or more variant alleles for a specific gene. For example: The KIT gene in horses is known for extensive polymorphism.

  • Points - In horses the lower legs, ear rims, mane and tail. For example: A bay horse with be reddish brown with black points.

  • Pheomelanin - The lighter form of melanin responsible for red, buff, tan and golden tones.

  • Phenotype - The physical appearance of an individual. As opposed to genotype. For example: Bay, black, brown, and buckskins are all different horse color phenotype.
• Q
• R

  • Recessive - When one allele is completely masked by another allele of a gene. For example the red(e) allele of extension is completely recessive to the black(E) allele.
• S

  • Somatic - Related specifically to the body. A somatic DNA mutation can not be inherited.
• T
• U
• V
• W
• X
• Y
• Z