The Tovero Paint Horse

Tob-overo Characteristics

1.  Tob-overo (tovero) horses have the characteristics of both the tobiano and overo horses.  You should read the tobiano and overo characteristics and genetics before you try to understand the tob-overo horses they are quite complicated but I will do my best to explain the different possibilities.

Tob-overo Genetics

First of all, the tobiano and overo genes are on different locations in the DNA.  This means that a horse can have both the tobiano and overo genes and their characteristics.  One of the characteristics may be minimal, for example a 3 inch overo spot on their belly plus having the typical tobiano markings.  When breeding tobiano and overo crosses, be sure you look for both characteristics on every foal.  The following examples are assuming that the overo gene is dominant, based on the research which I have read.

Example 1

When breeding a heterozygous tobiano with no overo characteristics or overo pedigree background may be represented by T t ø ø, we will make this horse the sire represented by the color blue.  The dam will be an overo represented by t t O ø with no tobiano characteristics.

There are four different combinations that the sire can produce with T t ø ø.  There are four combinations because each letter of the tobiano gene has to be paired with each letter of the overo gene

1.  T ø - This is the capital T matched up with the first ø.

2.  T ø - This is the capital T matched up with the second ø.

3.  t ø - This is the lower case t matched up with the first ø.

4.  t ø - This is the lower case t matched up with the second ø.

There are four different combinations that the dam can produce with t t O ø.   There are four combinations because each letter of the tobiano gene has to be paired with each letter of the overo gene.

1.  t O - This is the first lower case t with the first O.

2.  t ø - This is the first lower case t with the second ø.

3.  t O - This is the second lower case t with the first O.

4.  t ø - This is the second lower case t with the second ø.

Since there are four different possible combinations of genes from each parent there are 16 possible chances for the offspring in the yellow boxes (4 x 4 = 16).  The letters in the yellow boxes are color coded with pink and blue depending on which parent the offspring got those genes from.  These 16 possibilies may repeat, so there is more than one chance of getting that particular color.  In this example there are four toveros, four overos, four tobianos and four solid breeding stocks.  There is a 25% chance of getting a tob-overo (tovero), a 25% chance of getting an overo, a 25% chance of getting a tobiano and a 25% chance of getting a solid breeding stock.   Notice that the terminology has changed to solid rather than non-overo or non-tobiano, as on the tobiano and overo pages, because the tobiano and overo horses have been already accounted for on this page.

Example 2

When breeding a tob-overo horse to a solid horse, such as a quarter horse, it is possible to get a tobiano foal, an overo foal, a tob-overo foal or even a solid foal.  In table 2 the sire is a tob-overo (TtOø) horse and the mare is a solid quarter horse mare (ttøø).  The tob-overo (TtOø) sire has four different combinations which he can produce.

1. TO - The capital T (tobiano) is matched with the O (overo) gene.

2. Tø - The capital is matched with the ø (non-overo) gene

3. tO - The lower case t (non-tobiano) is matched with the O (overo) gene.

4.  t ø - The lower case t (non-tobiano) is matched with the ø (non-overo) gene.

The dam, a solid quarter horse (ttøø), also has four possibilities for the foal they are tø, tø, tø, and tø.  All she could produce on her own would be solid horses if she where bred to only solid horses, unless she had a cropout overo - which is very rare.

The offspring have a 25% chance of being tobiano, 25% chance of being overo, 25% chance of being a tob-overo (tovero) and a 25% chance of being solid.

Example 3

Lethal white is still a problem when you breed a tob-overo (tovero) horses crossed with an overo horse or a tob-overo horse.  In table 3, I am going to cross two tob-overo (tovero) horses, each being TtOø. 

Since both horses are the same they will each have the same four possibilities.

1. TO - The capital T (tobiano) is matched with the O (overo) gene.

2. Tø - The capital is matched with the ø (non-overo) gene

3. tO - The lower case t (non-tobiano) is matched with the O (overo) gene.

4.  t ø - The lower case t (non-tobiano) is matched with the ø (non-overo) gene.

There are several different combinations which may occure for the offspring.  I have listed the different compinations below for example 3.

1.  There is a 25% = [(4/16) x 100] chance of getting a lethal white foals.  These foals inherited an overo (O) gene from each of their parents.  These lethal white foals will usually die within 48 hours of birth.

2.  There is a12.5% = [(2/16) x 100] chance of getting a homozygous tobiano which also has the overo gene T T O ø.  If this horse was ever bred, when mature, they would produce all tobiano foals and also produce some tob-overo foals when bred to solid mares. 

3.  There is a 6.25% = [(1/16) x 100] of being a Homozygous tobiano without the overo gene T T ø ø.  

4.  There is a 25% = [(4/16) x 100] chance of getting a tob-overo foal with both the tobiano and overo genes.

5.  There is a 12.5% = [(2/16) x 100] chance of producing a heterozygous tobiano foal.

6.  There is a 12.5% = [(2/16) x 100] chance of producing an overo foal.

7.  There is a 6.25% = [(1/16) x 100] chance of producing a solid breeding stock foal.

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