The Tobiano Paint Horse

Tobiano Characteristics

1.  White will cross the back between the withers and the dock of the tail. 

2.  Generally all four of the tobiano's legs are white, at least below the hocks and knees.

3.  They will have face markings of a normal horse, such as a star, snip, strip, blaze or no marking at all on the face.

4.  The spots are rounded or oval shapes and generally the dark color will extend down the neck, giving the appearence of a shield.  It is typical for the dark color to  cover at least one of  the flank areas.

5.  The tail often has two colors.

6.  Tobiano horses can be predominantly dark or white in appearance.

Tobiano Genetics

The tobiano gene is dominant, meaning that if the horse has tobiano characteristics then the horse does have the tobiano gene.  If the horse does not express the tobiano genetics then the horse does not have the tobiano gene. 

A tobiano horse can be either "double gened or single gened" for this dominant trait.  The double gened tobiano horses are referred to as homozygous and should produce 100% colored tobiano offspring.  All of their foals will have the tobiano gene.  On the other hand a single gened tobiano is heterozygous for the dominant gene.  This horse will produce 50% colored tobiano offspring and 50% non-tobiano offspring when bred to non-tobiano mares.  Non-tobiano horses are either solid horses or overo colored horses. 

I am going to represent the dominant tobiano gene with a capical "T" and the non-tobiano resessive gene with a lower case "t".  Since each horse has two genes (one from each parent) the combinations which are possible are;

1.  TT - homozygous (100% color producer) tobiano

2.  Tt or tT - heterozygous tobiano which has the color but is not a 100% color producer for the tobiano gene

3.  tt - a non-tobiano horse which does not posess the tobiano gene at all.

Example 1

Below there is an example of crossing a heterozygous tobiano with a non-tobiano horse.  In Table 1, the sire is represented by the blue "T t" combination.   Since each of  his offspring will only recieve one of his genes, only one gene is passed onto the next generation represented by the four yellow boxes.  Each of these four boxes repesents a chance of recieving either one of his genes, one is tobiano (T) and the other is non-tobiano (t).   The dam is represented by the pink letters "t t", she is a non-tobiano horse and does not carry the tobiano gene.   With this cross, there is a 50% chance that the offspring will be colored tobiano and a 50% chance that the offspring will be a non-tobiano foal.  The yellow boxes represent chances, it is like flipping a coin, the more times you flip the coin the closer you will be to the 50% heads and 50% tails ratio.  Yes it is true, you could get 75% heads and 25% tails or even 100% heads but you would have to be very lucky.

Example 2

When crossing a homozygous tobiano with any non-tobiano horse you will always get color.  Table 2 illustrates why this is true.    If the homozygous tobiano is either a mare or a stallion the results would be the same.  In this example the sire is a homozygous tobiano represented by "T T" and the dam is a non-tobiano horse represented by "t t".

Example 3

When crossing two heterozygous (single gened) tobianos, use Table 3 as a visual example, there are several different combinations that you can get.  You have a 25% chance of getting a homozygous foal (T T), a 50% chance of getting a heterozygous tobiano (t T or T t), and a 25% chance of getting a non-tobiano foal (t t).  Overall there is a 75% chance of getting tobiano color and a 25% chance of getting non-tobiano foal.

Example 4

When breeding two tobiano horses, one is a homozygous and the other is a heterozygous you will have 100% colored foals which is good, as in table 4.  There is something even more important, you have a 50% chance of getting a homozygous foal and a 50% chance of getting a heterozygous foal. 

Example 5

Table 5, crosses two homozygous tobiano horses.  This will only produce homozygous tobiano offspring. 

If you have any questions, comments or suggestions you can e-mail me at breeze@turbonet.com.