Sire Roan Chestnut on dam Roan Dark Brown
In this article, we will explore the genetic possibilities of coat colors for the crossing between a stallion Roan Chestnut and a mare Roan Dark Brown. Equine genetics is a universe of combinations where dominant and recessive alleles determine the final coat of each individual.
On one side, we have the stallion Roan Chestnut. Genetically, it presents the base genotype e/e Rn/n. The (Rn) gene acts on the base coat by distributing white hairs throughout the body, giving it a roan appearance. The head and legs retain the original base color tones. This coat is based on Chestnut.
On the other side, the mare Roan Dark Brown contributes with its genetics based on E/_ A/_ Rn/n. The (Rn) gene acts on the base coat by distributing white hairs throughout the body, giving it a roan appearance. The head and legs retain the original base color tones. This coat is based on Dark Brown.
Quando combinamos esses códigos genéticos, criamos uma matriz de probabilidades. É importante lembrar que o resultado visual (fenótipo) muitas vezes esconde genes recessivos que podem pular uma geração.
The Genotypes Involved
For a horse to have the coat Roan Chestnut. it carries specific gene combinations. The possible genotypes for the sire include variants such as: e/e A/A Rn/n, e/e A/A Rn/Rn, e/e A/a Rn/n, e/e A/a Rn/Rn, e/e a/a Rn/n, e/e a/a Rn/Rn.
As for the dam, being Roan Dark Brown, may present in its DNA the alleles: E/e A/a Rn/n, E/e A/a Rn/Rn, E/e A/A Rn/n, E/e A/A Rn/Rn, E/E A/a Rn/n, E/E A/a Rn/Rn, E/E A/A Rn/n, E/E A/A Rn/Rn.
Understanding the Alleles
To understand the result of this crossing, note the gene sets at play:
- e/e (Red Factor - Homozygous Recessive): Determines the inability to produce black pigment, resulting in an exclusively red base coat (Chestnut).
- E/ (Extension - Dominant): The Extension gene controls eumelanin (black) production. At least one E allele allows the horse to have black hairs.
- A/ (Agouti - Dominant): The Agouti gene controls black distribution. The A allele restricts black pigment to the points (mane, tail, legs).
- a/a (Non-Agouti - Recessive): Allows black pigment to spread uniformly across the body. Essential for Solid Black (if E/).
- Rn/ (Roan - Rosilho): Mixes white hairs throughout the body, keeping head and extremities in the original color.
Calculated Probabilities
Being the sire Roan Chestnut with genotype (e/e A/A Rn/n), it transmits the (e) allele to 100% of offspring, allowing only red pigment expression (phaeomelanin) and transmits the (A) allele to 100% of offspring, restricting black pigment to the extremities and has a 50% chance of transmitting the Roan allele (Rn).
Being the sire Roan Chestnut with genotype (e/e A/A Rn/Rn), it transmits the (e) allele to 100% of offspring, allowing only red pigment expression (phaeomelanin) and transmits the (A) allele to 100% of offspring, restricting black pigment to the extremities and always transmits the Roan allele (Rn).
Being the sire Roan Chestnut with genotype (e/e A/a Rn/n), it transmits the (e) allele to 100% of offspring, allowing only red pigment expression (phaeomelanin) and transmits the (A) allele (restriction) to 50% and the (a) allele (no restriction) to the other 50% and has a 50% chance of transmitting the Roan allele (Rn).
Being the sire Roan Chestnut with genotype (e/e A/a Rn/Rn), it transmits the (e) allele to 100% of offspring, allowing only red pigment expression (phaeomelanin) and transmits the (A) allele (restriction) to 50% and the (a) allele (no restriction) to the other 50% and always transmits the Roan allele (Rn).
Being the dam Roan Dark Brown with genotype (E/e A/a Rn/n), it transmits the (E) allele (black factor) to 50% and the (e) allele (red factor) to the other 50% and transmits the (A) allele (restriction) to 50% and the (a) allele (no restriction) to the other 50% and has a 50% chance of transmitting the Roan allele (Rn).
Being the dam Roan Dark Brown with genotype (E/e A/a Rn/Rn), it transmits the (E) allele (black factor) to 50% and the (e) allele (red factor) to the other 50% and transmits the (A) allele (restriction) to 50% and the (a) allele (no restriction) to the other 50% and always transmits the Roan allele (Rn).
Being the dam Roan Dark Brown with genotype (E/e A/A Rn/n), it transmits the (E) allele (black factor) to 50% and the (e) allele (red factor) to the other 50% and transmits the (A) allele to 100% of offspring, restricting black pigment to the extremities and has a 50% chance of transmitting the Roan allele (Rn).
Being the dam Roan Dark Brown with genotype (E/e A/A Rn/Rn), it transmits the (E) allele (black factor) to 50% and the (e) allele (red factor) to the other 50% and transmits the (A) allele to 100% of offspring, restricting black pigment to the extremities and always transmits the Roan allele (Rn).
Based on a standard scenario, the statistical chances for foals from this crossing are:
Roan BayOpen Coat ➜ 38,1%
Roan ChestnutOpen Coat ➜ 26,3%
BayOpen Coat ➜ 12,7%
ChestnutOpen Coat ➜ 8,8%
Roan BlackOpen Coat ➜ 6,4%
Roan Dark BrownOpen Coat ➜ 4,2%
BlackOpen Coat ➜ 2,1%
Dark BrownOpen Coat ➜ 1,4%
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