The Overo coat pattern is a white spotting pattern with white patches on the side with a “frame” of colour surrounding the white. A horse can also carry mutations for other modifying genes which can further affect its coat colour. Si bien los caballos de color Overo son deseables, la mutación que causa el color overo está vinculada a una condición fatal conocida como Síndrome de Overo Lethal White o OLWS. Un potro con OLWS nace todo blanco y muere por complicaciones de anomalías del tracto intestinal. La prueba Color de Capa Overo (P902) analiza un factor genético que afecta la función del gen EDNRB. Este gen tiene dos variantes (alelos). El alelo O es semi-dominante. Una copia del alelo O da como resultado caballos con patrón de capa overo. Dos copias del alelo O resultan en un potro blanco letal (OLWS). El alelo N es recesivo y no tiene efecto en el color básico.
The Coat Colour Overo-factor test encloses the following results, in this scheme the results of the Coat Colour Overo-factor test are shown in combination with the possible results for the tests that determine the basic Coat Colour (Coat Colour Chestnut and Coat Colour Agouti test):
|
Result Overo-factor |
Result Chestnut + Agouti |
Coat Colour |
Descripción |
|---|---|---|---|
|
N/N |
e/e + A/A, A/a or a/a
|
Chestnut, Sorrel
|
Not Overo. The basic colour chestnut/sorrel is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring. |
|
N/N |
E/E or E/e + A/A or A/a |
Bay, Brown |
Not Overo. The basic colour bay/brown is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring. |
|
N/N |
E/E or E/e + a/a |
Black |
Not Overo. The basic colour black is not modified unless modified by other colour modifying genes. It can only pass on allele N to its offspring. |
|
N/O |
e/e + A/A, A/a or a/a
|
Chestnut/sorrel overo |
Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring. |
|
N/O |
E/E or E/e + A/A or A/a |
Brown/bay overo |
Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring. |
|
N/O |
E/E or E/e + a/a |
Black overo |
Overo pattern. One copy of the O allele. The horse has the desirable frame overo pattern unless modified by other colour modifying genes. It can pass on either allele N or O to its offspring. |
|
O/O |
Any result |
Lethal (OLWS) |
Foal with Overo Lethal White Syndrome (OLWS), lethal. |