Colour Genetics 2: Base Colours
In this second posting of the Colour Genetics series, we will go over the base colours that are seen in horses, and the genes that are at play. If you haven't seen it already, I recommend looking at the first post in the series, as it goes over the basics of genetics, especially if you aren't too familiar with the field or need a touchup!
Horses come in 3 base colours; Black, Chestnut, and Bay, and are dictated by 2 genes and how they affect each other. Other colours, which are other genes interacting with these two, will be discussed in future posts.
The first gene "E" serves as the base colour, and the form (E) is dominant over the recessive form (e). This gene is called "E" for "Extension" which determines wether or not eumelanin can be produced or not. Eumelanin is the "true" black pigment. Horses with E/E or E/e are capable of producing eumelanin (as you only need one functional allele in order for this gene to be expressed, but this isn't true for all genes) and e/e horses aren't. This means that both E/E and E/e horse's bases are black, and e/e horses have a chestnut base. This is because the e/e horses are still capable of producing pheomelanin, a reddish pigment, as this is the default pigment produced by the cells unless triggered to do otherwise by the active Extension allele. Chestnut horses at birth may have pink skin and blue eyes, but barring any other gene interactions, this usually goes away as the horse matures, and like black horses they will have black skin and brown eyes.
The second gene "A", for Agouti, is a modifier and controls the distribution of eumelanin. A is dominant over a, and when present, it restricts the pigment to the points of the horse. The points are the face (typically around the nose and eyes), lower legs, mane and tail, and along the back. Because this gene only affects eumelanin, horses that can't produce it and only produce pheomelanin (e/e horses) are unaffected by this gene. So whilst e/e horses won't be visually affected by the Agouti gene, they can still be carriers for it and pass it on to their offspring.
The Agouti gene restricting eumelanin is what is responsible for dark brown and bay horses. Some research shows that there may potentially be a correlation between E/E horses being dark bay and E/e horses being a light bay (when they also carry the "A" gene).
Horses come in 3 base colours; Black, Chestnut, and Bay, and are dictated by 2 genes and how they affect each other. Other colours, which are other genes interacting with these two, will be discussed in future posts.
The first gene "E" serves as the base colour, and the form (E) is dominant over the recessive form (e). This gene is called "E" for "Extension" which determines wether or not eumelanin can be produced or not. Eumelanin is the "true" black pigment. Horses with E/E or E/e are capable of producing eumelanin (as you only need one functional allele in order for this gene to be expressed, but this isn't true for all genes) and e/e horses aren't. This means that both E/E and E/e horse's bases are black, and e/e horses have a chestnut base. This is because the e/e horses are still capable of producing pheomelanin, a reddish pigment, as this is the default pigment produced by the cells unless triggered to do otherwise by the active Extension allele. Chestnut horses at birth may have pink skin and blue eyes, but barring any other gene interactions, this usually goes away as the horse matures, and like black horses they will have black skin and brown eyes.
The second gene "A", for Agouti, is a modifier and controls the distribution of eumelanin. A is dominant over a, and when present, it restricts the pigment to the points of the horse. The points are the face (typically around the nose and eyes), lower legs, mane and tail, and along the back. Because this gene only affects eumelanin, horses that can't produce it and only produce pheomelanin (e/e horses) are unaffected by this gene. So whilst e/e horses won't be visually affected by the Agouti gene, they can still be carriers for it and pass it on to their offspring.
The Agouti gene restricting eumelanin is what is responsible for dark brown and bay horses. Some research shows that there may potentially be a correlation between E/E horses being dark bay and E/e horses being a light bay (when they also carry the "A" gene).
Comments
Post a Comment