Welcome to the most advanced Coat Colour Calculator available online. Whether you are breeding horses, dogs, or livestock, understanding Mendelian inheritance is key to predicting the visual outcome of your next generation.
Sire (Male) Genotype
Dam (Female) Genotype
A) What is a Coat Colour Calculator?
A coat colour calculator is a specialized tool used by animal breeders to determine the statistical likelihood of specific colors appearing in offspring. It operates on the principles of Mendelian genetics, specifically focusing on dominant and recessive alleles. In most mammals, the foundation of all colors is determined by two primary genes: the Extension (E) gene and the Agouti (A) gene.
By inputting the known genotypes of the sire and dam, the calculator runs a series of Punnett square simulations to output the percentage chance of each color variation, such as Bay, Black, or Chestnut in horses, or similar patterns in other species.
B) The Formula and Genetic Explanation
The logic behind the calculator follows the rule of independent assortment. Each parent contributes one allele per gene to the offspring.
| Gene | Dominant Allele (Uppercase) | Recessive Allele (Lowercase) |
|---|---|---|
| Extension (E) | E: Produces black pigment. | e: Produces red (phaeomelanin) pigment. |
| Agouti (A) | A: Restricts black to "points" (ears, legs, tail). | a: No restriction; allows black over the whole body. |
The basic phenotypes are derived as follows:
- Bay: At least one 'E' and at least one 'A' (E_ A_).
- Black: At least one 'E' but two recessive 'a's (E_ aa).
- Chestnut/Red: Two recessive 'e's (ee __). Note: Agouti does not show on red coats.
C) Practical Examples
Example 1: The "Surprise" Red. If you breed two Black horses that are both heterozygous for Extension (Ee aa x Ee aa), there is a 25% chance of producing a Chestnut (ee aa) foal. This often surprises breeders who don't realize their black horses carry the "hidden" red gene.
Example 2: Purebred Bay. Breeding a Homozygous Bay (EE AA) to any other base color will result in 100% Bay offspring, as the dominant 'E' and 'A' will always be present in the offspring's genotype.
D) How to Use the Calculator Step-by-Step
- Identify Parent Genotypes: Use DNA test results if available. If not, infer based on their parents or previous offspring.
- Select Sire Extension: Choose between EE, Ee, or ee.
- Select Sire Agouti: Choose between AA, Aa, or aa.
- Repeat for Dam: Input the mother's genetic profile.
- Analyze Results: The calculator will instantly display the probability of each phenotype and provide a visual chart.
- Export: Click "Copy Results" to save the data for your breeding records.
E) Key Factors Influencing Coat Colour
While Extension and Agouti are the "base" genes, several other factors can modify the final appearance:
- Dilution Genes: Genes like Cream (Cr), Dun (D), and Silver (Z) can lighten the base color.
- White Patterns: Genes like Tobiano or Overo can add white patches over the base color.
- Epistasis: This occurs when one gene masks the expression of another (e.g., 'ee' masking the 'A' gene).
F) Frequently Asked Questions (FAQ)
1. Can two black horses produce a bay foal?
No. Black horses are 'aa'. Since both parents are 'aa', they cannot pass on a dominant 'A' allele, which is required for a horse to be Bay.
2. What does "Homozygous" mean?
It means the animal has two identical alleles for a gene (e.g., EE or ee). "Heterozygous" means they have two different alleles (e.g., Ee).
3. Is chestnut recessive to black?
Yes. The 'e' allele is recessive. An animal must have two copies (ee) to appear chestnut/red.
4. Does the calculator work for dogs?
While the basic E and A loci exist in dogs, canine genetics is more complex with the K locus (Dominant Black). This calculator is optimized for equine base colors but uses the same Mendelian logic applicable to many species.
5. Why did my Bay parents have a Chestnut foal?
Both parents must have been carriers of the red gene (Ee). When both pass the 'e' allele, the offspring is 'ee' (Chestnut).
6. How accurate are these predictions?
The predictions are 100% mathematically accurate based on the inputs. However, if the parent genotypes are guessed incorrectly, the results will differ.
7. What is the "Wild Bay" allele?
It is a variation of the Agouti gene (A+) that restricts black even further than the standard 'A' allele, often seen in Przewalski's horses.
8. Can a Chestnut horse carry Black?
A Chestnut horse (ee) can carry the Agouti gene (A), but since they cannot produce black pigment, you won't know they have it unless you DNA test or look at their offspring.