Horse Color Calculator (Equine Coat Color Genetics & Alleles)
Predict offspring foal coat colors using Extension (E/e) and Agouti (A/a) genetics across Chestnut, Bay, and Black horse pairings.
Calculator Parameters
Calculated Results
🏢 Request Project Parameters & Verified Quote
Free Local InquiryCompare verified rates, customized parameters, and specialist estimates for your calculation without obligation.
How to Use the Horse Color Calculator (Equine Coat Color Genetics & Alleles)
Breeding horses involves fascinating Mendelian genetics governed by two primary genes: the Extension gene (which controls black vs. red pigment) and the Agouti gene (which controls where that black pigment is distributed across the body).
Our Horse Color Calculator calculates the probability of producing Bay, Chestnut, and Black foals based on the sire and dam's phenotype and known zygosity, clarifying how recessive traits and epistatic masking work.
Formula and Calculation Methodology
- Extension (E): Dominant E produces black pigment; recessive ee produces red (Chestnut)
- Agouti (A): Restricts black pigment to points (mane, tail, legs) producing Bay; aa leaves coat pure Black
- Epistasis: A horse with 'ee' will ALWAYS be Chestnut regardless of what Agouti genes it carries
Applies standard Mendelian inheritance matrices across the MC1R (Extension) and ASIP (Agouti) equine genetic loci.
Base Equine Coat Color Punnett Square
| Genotype | Base Color | Extension Allele | Agouti Allele |
|---|---|---|---|
| E_ A_ | Bay | At least one dominant E | At least one dominant A (restricts black) |
| E_ aa | True Black | At least one dominant E | Recessive aa (black all over) |
| ee A_ or ee aa | Chestnut / Sorrel | Recessive ee (no black pigment) | Masked (cannot restrict red pigment) |
Frequently Asked Questions
Can two chestnut horses produce a bay or black foal?
No. Chestnut is caused by the homozygous recessive genotype 'ee'. Because two chestnut parents have only recessive 'e' alleles to pass down, 100% of their offspring will be chestnut (ee).
What makes a bay horse different from a black horse genetically?
Both bay and black horses have at least one dominant Extension allele (E), allowing them to produce black pigment. However, a bay horse has a dominant Agouti allele (A) that restricts black to the points (legs, mane, tail), while a black horse has recessive 'aa' allowing black pigment throughout the coat.
Can a chestnut horse carry the agouti gene?
Yes! A chestnut horse can carry dominant Agouti alleles (e.g. ee Aa or ee AA), but because they have no black pigment to restrict, the Agouti gene is hidden (epistasis). If bred to a black horse, they can pass this Agouti gene down to produce a bay foal.
How do dilution genes like Cream or Dun affect these base colors?
Dilution genes modify base colors. For example, a single Cream gene (Cr) turns Chestnut into Palomino, Bay into Buckskin, and Black into Smoky Black.
What is the difference between Chestnut and Sorrel?
Genetically, Chestnut and Sorrel are identical ('ee'). In Western stock horse registries (like AQHA), lighter copper-red coats with matching or flaxen manes are called Sorrel, while darker liver-red coats are called Chestnut.
🔗 Related Calculators & Tools
North Node Calculator
True and mean lunar node astrological sign and house.
Crop Nutrient Removal Calculator
Soil fertility, N-P-K-S removal pounds per acre.
Punnett Square Calculator
Genotype and phenotype probability distribution.
Cat Age Calculator
Feline life stages and human-equivalent years.