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Normal Coat Color Development

During embryogenesis, precursor cells migrate through the whole body, and when reaching their destination they differentiate into cells with certain tasks. Some of these precursor cells will differentiate to pigment producing cells called “melanocytes”. This process of migration and differentiation is controlled by genes. Usually it can be separated in the following chronological steps:

1. Pigment producing cells reach their destination during embryogenesis.
2. Cells produce pigments.
3. Pigments are transported into hair.
4. Cells stay vital and keep producing pigments.


If things do not run “according to plan”…

Changes in this chronological order may lead to different coat patterns. Changes might be:

1. Melanocytes (pigment producing cells) do not reach their destination.
2. Cells are nonfunctional and cannot produce any pigment.
3. Produced pigment cannot be transported into/stored in hair.
4. Melanocytes “burn out” and gradually die after differentiation (greying).


All these changes result in white patches but are caused by different genetic mechanisms. Genes are often pleiotropic. That means that a single gene influences many traits. Consequently, mutations may not only change phenotype and pattern but may also influence health.

The different Patterns

Depending on which mechanisms of coat color development are disturbed, different patterns are displayed. Often horses inherit several patterns simultaneously which makes it difficult to identify all inherited pattern mutations. Visit the respective pages for further information on the different patterns and their genetic causes.

Silvery Moon xx                                  ©Gille

“Silvery Moon xx” is an excellent example of a bay frame overo with a high amount of white. See his test results for explanations (with kind permission from the Haupt- und Landgestüt Marbach):

f.l.t.r.: likely Frame Overo and possible splashed white, Leopard Complex, Leopard Complex with dilution.

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