Homozygous Tobianos:
A true homozygous Paint horse is always a tobiano. The homozygous horse
has two identical tobiano genes and must be sired by a tobiano, and have
a tobiano for a mother. The true homozygous tobiano must have secondary
body spotting called "ink spots" and "paw prints" and must never have produced
any solid colored foals from solid colored mates. Homozygous Tobianos will
always pass a tobiano gene to an offspring (genes TT). The majority of
homozygous tobiano stallions standing today, sire 100% tobiano paint
colored foals from the mares they breed. A few horses that are listed as
homozygous, have sired the occasional solid breeding stock foal,
but this is rare.
What does "Informative" and "Uniformative" mean?
In a horse classified as "informative", the blood markers of the
individual can be used as indicators to test their offspring for
homozygous tobiano status. In an "uninformative" horse, the
blood markers of this individual do not confirm the tobiano status
of their foals, so the ability of this horse to consistently sire or
produce colored foals, cannot be determined.
To determine if a horse is homozygous, you must evaluate the following:
1. Pedigree: Both parents must be tobiano or Tovero.
2. Phenotype: The horse should have secondary body spotting such
as "ink spots" or "paw print".
Ink Spots, Paw Print Markings: These unique and distinctive markings are
usually located in the 'white' hair areas on a tobiano and are small dabs of
spots or color (1-3 inches) surrounded with prominent "blue zones"
(white hairs on black pigmented skin that give the hair a blue appearance)
surrounding the 'spot'. Usually there will be groups of prints that look like
dog or cat tracks.
3. Test Breeding: The horse should have no solid offspring from solid mates.
4. Studbook Data: The horse has no solid offspring.
5. Genetic Marker Analysis: Genetic testing by approved laboratory.
The Blood Markers: All equine parentage was originally
verified through blood typing. Although researchers have never been able
to identify a "color" gene, they were able to trace blood markers passed
from the parent to the offspring for tobiano Paint horses. Studies were conducted
on tobiano mares and stallions, and their resultant offspring. These studies led to
the discovery of blood markers that are 'linked' to the tobiano gene. The
prevalent theory is that the genes producing blood type are very close in
location to the tobiano gene. Subsequently, when the gene for a blood type
is passed along, the tobiano gene located next to it will be passed along to
the foal, too. This process has been labeled 'linkage', and it makes the
identification of tobiano status possible in foals from informative parents.
Test breeding on solid mares is used to confirm the status of individuals
thought to be homozygous, as it is possible for these genes to be
'unhooked' and not passed together.
The Homozygous "EE" Black Horse
What is the Homozygous Black Gene?
The red coat color in horses is inherited as a trait recessive to black.
A blood test for the red factor, based on DNA analysis, provides the
information to determine what color offspring a horse can throw.
The absence of the red factor presents itself as "E".
"E" = no red factor detected. The horse can be assumed to be homozygous
for black pigment (EE). It cannot have red foals (chestnut or sorrel) regardless
of the color of the mate. The basic color of the horse will be black or bay,
but depending on genes at the other color loci, the horse may be buckskin,
zebra dun, grulla, perlino, gray, white or any of these colors with the
white hair patterns tobiano, overo, paint, roan or appaloosa.
FOR MORE INFORMATION ON HOMOZYGOUS
PLEASE GO TO THE FOLLOWING WEB SITES. . .
Double W Acres
Ryan Woltman ~ Owner
Heidi Woltman ~ Office/Farm Manager
46613 120th Street
Remsen, IA 51050
Tel & Fax: 712-786-1109
Heidi's Cell: 712-501-4029
