Sire Chestnut on dam Roan Chestnut
In this article, we will explore the genetic possibilities of coat colors for the crossing between a stallion Chestnut and a mare Roan Chestnut. 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 Chestnut. Genetically, it presents the base genotype e/e. Base coat with a reddish body, mane and tail, with no black pigment.
On the other side, the mare Roan Chestnut contributes with its genetics based on 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.
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 Chestnut. it carries specific gene combinations. The possible genotypes for the sire include variants such as: e/e A/A, e/e A/a, e/e a/a.
As for the dam, being Roan Chestnut, 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.
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).
- 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 Chestnut with genotype (e/e A/A), 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.
Being the sire Chestnut with genotype (e/e A/a), 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%.
Being the sire Chestnut with genotype (e/e a/a), it transmits the (e) allele to 100% of offspring, allowing only red pigment expression (phaeomelanin) and transmits the (a) allele to 100% of offspring, allowing black to spread in homozygosis (if Extension is present).
Being the dam 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 dam 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 dam 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 dam 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).
Based on a standard scenario, the statistical chances for foals from this crossing are:
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