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- there are 3 types of base coats that a horse can be: black, red [sorrel/chestnut], and bay [red with black points]. the mixing of the extension and agouti genes determines what base color the horse will be and how the dilution and/or white genes will alter their appearance. a horse needs a dominant allele of both the extension and agouti gene to come out as bay in color [ex. AA EE, AA Ee, Aa EE, Aa Ee]. if they have either one dominant allele for only one gene or no dominant alleles at all, then the will be classified as either black or red as explained below.
the extension gene;
- 'E/e' is the extension gene which is for determining if the horse is black [EE aa or Ee aa] or red [ee aa] based and affects all the other color genes. this gene is mostly for determining what color the horse's legs will be, which is why bay horses have dark points on the legs and face. if a horse has double recessive extension genes, then the horse is automatically a red based horse and is unable to be bay or black based.
the agouti gene;
- 'A/a' is the agouti gene which is responsible for the bay coloring [AA or Aa] due to the gene forcing the black to the points and showing the red body. this gene is mostly for determining what color the horse's body will be, black or red. if a horse has double recessive agouti genes, then they will be either red or black depending on the dominance of the extension gene.
writing the code;
- though it may look quite confusing and complex, writing out the genetic code for a horse is quite easy. first, you look at the base color, then you add on any dilutions the horse may have. it's easier to break it all down by steps. instead of thinking 'blue roan', think 'black base with roan' since this way you can put it together like this: black base [Ee aa or EE aa] with roan [RnRn or nRn]. so now you can just write it out: EE aa RnRn [i chose a higher chance of passing on the black and roan genes]
feel free to message me if you have any questions or difficulties.