PAINTED DESERT John Mule with a somatic mutation. Basically the gene responsible for brown color in that hair was switched off in that area and resulted in black hair. Somatic mutations are not inherited traits.
"Equine Color Genetics: This Trakehner colt, Holme Park Van Gogh, was an excellent example of a somatic mutation. The black patch on his otherwise bay coat was the result of the agouti gene misfiring leaving that section of his coat an undiluted black.
horse chimera:the bonding of fraternal twins in utero gives rise to unusual striping and brindle horses. DNA testing of a chimera will result in two completely different dna genes, and can even be different genders. It's literally two horses in one body.
Mosaic means she has the DNA of only 1 horse, but her bay gene was deactivated from expressing in that patch. If you did a gene test in her bay area, and a gene test in her black area they would be genetically identical. filly by Charge Forward