• 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
  

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