The Tobiano coat pattern usually involves white on all four legs below the hocks and knees and rounded white spots on the body with sharp, clean edges. The head is dark, with white markings like those of a solid colored horse. The white on the body will generally cross the top-line of the horse. The skin underlying the white spots is pink and under the colored areas it is black. The eyes are usually brown, but one or both may be blue or partially blue. The tail can be two colors, a characteristic seldom seen in horses that are not tobiano. A horse can also carry mutations for other modifying genes which can further affect its coat colour.

The Coat Colour Tobiano test (P903) tests for a genetic factor that affects the function of the KIT gene. This gene has two variants (alleles). The dominant allele TO results in the Tobiano pattern and the recessive allele N does not have an effect on the basic colour.

The Coat Colour Tobiano test encloses the following results, in this scheme the results of the Coat Colour Tobiano 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 Tobiano

Result Chestnut + Agouti

Coat Colour

Description

N/N

e/e + A/A, A/a or a/a

 

Chestnut, Sorrel

 

Not Tobiano. 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 Tobiano. 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 Tobiano. 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/TO

e/e + A/A, A/a or a/a

 

Chestnut/sorrel tobiano

One copy of the dominant TO allele. The colour is chestnut/sorrel tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

N/TO

E/E or E/e + A/A or A/a

Bay/brown tobiano

One copy of the dominant TO allele. The colour is bay/brown tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

N/TO

E/E or E/e + a/a

Black tobiano

One copy of the dominant TO allele. The colour is black tobiano unless modified by other colour modifying genes. It can pass on either allele N or TO to its offspring.

TO/TO

e/e + A/A, A/a or a/a

 

Chestnut/sorrel tobiano

Two copies of the dominant TO allele. The colour is chestnut/sorrel tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

TO/TO

E/E or E/e + A/A or A/a

Bay/brown tobiano

Two copies of the dominant TO allele. The colour is bay/brown tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

TO/TO

E/E or E/e + a/a

Black tobiano

Two copies of the dominant TO allele. The colour is black tobiano unless modified by other colour modifying genes. It can only pass on allele TO to its offspring.

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