DISCLAIMER: If there is incorrect information, please comment to let me know so I can fix it. However, if there is missing information, it is most likely intentional as this is meant to be very very basic. If you are that invested in equine genetics, there are many other helpful guides and explanations on DA, as well as the internet as a whole. This is meant for those who are confused and/or need a quick reference for what genes create what colors.
About the Agouti Gene In Bays: Agouti controls the restriction of true black pigment (eumelanin) in the coat. Horses with the normal agouti gene have the genotype A/A or A/a. Horses without a normal agouti gene have the genotype a/a, and if they are capable of producing black pigment, it is uniformly distributed throughout the coat. If they do not possess the dominant E gene, there is no black pigment in the horse to restrict, and therefore no black points will be seen in chestnut-based horses.
- a, the least dominant, must be homozygous to be observed and is responsible for unrestricted black coat (non-agouti black),
- At, only visible in the homozygous form or when paired with a, is responsible for the black-and-tan seal brown coat,
- A, visible when homozygous or when paired with a or At, is responsible for the standard bay coat,
- A+, dominant, is responsible for the wildtype wild bay coat
A+ is not mentioned above, but “Wild Bay” As it is called, is simply bay but restricts the black points on the legs to only reach the ankles. It is often paired with pangare, but is NOT responsible for any lightening of the coat. That is all Pangare.
If a horse is Homozygous, it means that it has two dominant alleles. EE is homozygous black. ChCh is homozygous champagne. CrCr is homozygous cream. Homozygous means that one copy will always pass to the horse’s offspring.
Example: ee aa CrCr = Cremello X ee aa = Chestnut
= ALWAYS has palomino foals: ee aa nCr
Example: Ee Aa ChCh = Amber champagne X Ee aa ChCh = Classic Champagne
= ALWAYS have ChCh foals. Possibly Amber Champange, Classic Champagne, or Gold Champagne.
This is because if you are choosing your foal’s genetics, you get to choose one of the two alleles for each gene. Ee you can choose E or e. For Aa you can choose A or a. But for homozygous genes you will have the same when you have ChCh.
Unfortunately there is much more information to be explained, such as wild bay, gene mutations like brindle and chimera, but again, this is meant to be as basic as possible. If you do have questions on genetics or help with possible foal colors, feel free to comment and ask here.