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Studijní materiály
Strakoši
AGA38E - Plemenitba koní
Vyučující: doc. Ing. Mgr. CSc. Ivan Majzlík
Zjednodušená ukázka:
Stáhnout celý tento materiál07CoatColorGenetics 12/14/07 6:51 PM Page A
Contents
The Genetic Equation of Paint Horses . . . . . . . . .IFC
Tobiano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Overo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Tovero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Breeding the Tobiano Paint . . . . . . . . . . . . . . . . . . .4
Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Understanding Simple Dominance . . . . . . . . . . . . .4
Using the Punnett Square . . . . . . . . . . . . . . . . . . . .4
Understanding genes, simple dominance
and the Punnett Square . . . . . . . . . . . . . . . . . . . .4
Breeding the Tobiano Paint . . . . . . . . . . . . . . . . . . .5
Determining Tobiano Homozygosity . . . . . . . . . . . .5
Breeding the Overo Paint . . . . . . . . . . . . . . . . . . . . .6
Breeding the Frame Overo . . . . . . . . . . . . . . . . . . . .6
Defining Minimal-White Frame Overo . . . . . . . . . .6
Breeding the Splashed White Overo . . . . . . . . . . . .6
Defining Minimal Splashed-White Overo . . . . . . . .6
Breeding the Sabino Overo . . . . . . . . . . . . . . . . . . .7
Defining Minimal-White Sabino Overo . . . . . . . . . .7
Breeding the Tovero . . . . . . . . . . . . . . . . . . . . . . . . .7
Coat Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
The Basic Rules of Coat Color Genetics . . . . . . . . . .9
Overo Lethal White Syndrome . . . . . . . . . . . . . . .16
Lethal Whites—Fact Versus Fiction . . . . . . . . . . . .16
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Color Description Guide . . . . . . . . . . . . . . . . . . . .BC
For more information on the
American Paint Horse Association
and what it can offer you,
call (817) 834-2742, extension 788.
Visit APHA’s official Web site at apha.com.
The Genetic Equation
of Paint Horses
Paint Horses are unique from most other breeds
because of their spotted coat patterns. Their base coats
are the same colors as those of other breeds, but super-
imposed over these colors are a variety of white spotting
patterns. The three patterns recognized by APHA are
tobiano, overo and tovero.
The ability to recognize these patterns and under-
stand the genetics behind them is essential for Paint
Horse breeders. Being knowledgeable about coat pat-
terns helps breeders and owners accurately describe
their horses. Understanding the genetics that produce
these patterns helps breeders increase the proportion of
spotted horses in their foal crops.
Following are descriptions of the major Paint Horse
spotting patterns.
07CoatColorGenetics 12/14/07 6:51 PM Page B
The second generally accepted type of
spotting is overo (pronounced: oh vair´ oh).
Knowing the history behind the term overo
may be helpful in understanding the some-
what confusing situation of having multiple
patterns with one name.
Overo is a Spanish word, originally mean-
ing “like an egg.” In this case, it refers to
speckling or spotting. Long ago, in South
America, the term overo was used for all the
various spotting patterns in horses: tobiano,
overo (all three types) and also the blanket
and leopard patterns typical of Appaloosas.
In Argentina, the word overo is still used to
describe all the different spotting patterns
other than tobiano.
In the United States, overo is usually used
to mean “Paint, but not tobiano.” This has
resulted in the lumping together of three
different spotting patterns under one name,
and the result can be confusion in breeding
programs.
The term overo covers three genetically
distinct patterns: frame overo, sabino and
splashed white.
Frame Overo
The name “frame” refers to the usual
appearance, which is of white patches cen-
tered in the body and neck, and framed by
colored areas around them.
The usual frame pattern has a horizontal
arrangement and does not cross the topline,
as does tobiano. The overo’s head is usually
quite extensively marked with white and the
eyes are commonly blue.
The feet and legs of frame overos are usu-
ally dark, although white feet and minor
The first major pattern is tobiano (pro-
nounced: tow be yah´ no). The name tobiano
is itself unusual and has an interesting
history. In Argentina, it is the habit to name
unusual colors after horses or people who
connect the color to a specific event or indi-
vidual. In the case of the tobiano horse, that
event was the rescue of Buenos Aires by
Brazilian General Tobias during a military
action that took place in the 1800s. Many of
the troops with Tobias were mounted on
tobiano spotted horses from Brazil.
This color pattern had occurred only rarely
in Argentina before this event (and was
lumped in with all the other spotting patterns
as overo), but became firmly associated with
Tobias and his troops afterwards, ending up
taking his distinctive name.
The tobiano pattern occurs in many
breeds worldwide. It is common in pony
breeds, some draft breeds and even
occurs in some of the warmblood breeds.
In some breeds, tobiano spotting disquali-
fies a horse for inclusion in the registry—
this in spite of the fact that the trait may
have been present in some of the founda-
tion horses from which the breed sprang.
The characteristics of tobiano
A tobiano’s feet and varying portions of
its legs are usually white, the head usually
has no more white than normally found on
a non-spotted horse, and the spots usual-
ly cross the topline somewhere between
the ears and tail.
Tobiano spots are typically crisply delineat-
ed from the colored areas and have a vertical
arrangement. A tobiano’s
eyes are usually dark.
These horses can vary
from quite dark, with only small
amounts of white, to quite white, with little
remaining color. The darker individuals some-
times have so little white spotting that they
may be confused with nonspotted horses.
Minimally spotted tobianos are interest-
ing because they are essentially tobianos
that did not get spots. These horses will
produce just like a spotted horse, however,
and that is the reason the pattern may
“mysteriously” appear in a breeding pro-
gram for solid horses.
A clue to identifying these “nonspotted
tobianos” is that they tend to have a large
amount of white on the lower legs but little
white on the head. This combination is oth-
erwise rare because it is usually the case
that non-spotted horses with a great deal
of white on the head have a large amount
of white on the feet, and vice versa.
In the middle portion of the range of
tobiano spotting there is no problem telling
tobianos from other Paint patterns. They are
quite distinctive. At the whitest extreme,
many tobianos are all white except for a col-
ored head. This pattern is sometimes called
“Moroccan,” although the connection to the
country of Morocco or its horses is tenuous
at best.
Other details of the tobiano pattern include
the fact that on many of these horses, the
border between the white and colored areas
consists of pigmented skin overlaid by white
hairs. The result is usually a bluish cast to
the border, almost like a halo or a shadow.
Another peculiarity of some tobianos is the
presence of “ink spots” in the white patch-
es. These spots are small and generally
round in shape.
APHA Coat Color Genetics Guide • 1
Tobiano
Overo
Typical Tobiano Patterns
Typical Overo Patterns
Tobiano
07CoatColorGenetics 12/14/07 6:51 PM Page 1
white leg marks are as common on frame
overos as they are on nonspotted horses.
The white areas on frame overos are usual-
ly crisply and cleanly delineated from the
colored areas, although some have a halo or
shadow of pigmented skin under white hair
directly at the boundary.
The frame overo pattern occurs in a lim-
ited range of horse breeds. It seems to
appear only in breeds that have Spanish
ancestry, including the Paint Horse.
The genetics of frame overo has only
recently been documented. Frame overo
behaves as a dominant gene. It is common
to mate frame overo horses to nonspotted
horses, and about half of the resulting foals
are spotted.
On many occasions, though, there are
records of frame overos being produced by
two nonspotted parents. This is typical of a
recessive gene, and it is not logical to have
both a recessive and a dominant control
over the same pattern.
Some of these horses are genetically frame
overo, but have failed to get a body spot. They
are essentially very dark frame overos—so
dark that the spots are all gone from the body.
They still have the gene, however, and can still
produce frame overo-spotted offspring.
At the whiter extreme, frame overo is the
pattern most closely associated with Overo
Lethal White Syndrome (see page 16).
Recent characterization of the gene
responsible for lethal white foal syndrome
has confirmed that foals with two doses of
the lethal white gene are white and die soon
after birth from gut innervation abnormali-
ties. Horses with only one dose survive.
This documentation is important for
Paint Horse breeders. With DNA tests now
available to identify the lethal white gene, it
is possible to test breeding horses. Those
with the gene can be
mated to horses with-
out it, resulting in
foals that are about
half carriers and half-
non-carrier foals, but avoiding completely
the production of lethal whites.
Sabino Overo
In literal Spanish, sabino (pronounced:
sah bee´ no) means pale or speckled. In
Europe, and increasingly in the United
States, sabino is used to describe a unique
and interesting pattern of white spotting in
horses.
Sabino horses usually have four white feet
and white legs. The white usually extends
up the legs in ragged patches, and then
extends onto the horse’s body from the belly.
The head is usually fairly white and the eyes
are commonly blue.
Many sabino horses have partially blue,
partially brown eyes. Flecks, patches and
roan areas are common on sabinos, in con-
trast to the frame overos, which are usually
more crisply marked.
Sabino occurs in a large num-
ber of breeds worldwide,
including Paints, Thorough-
breds and Clydesdales. The pat-
tern is commonly the cause of
spotted foals that appear in
breeds that frown on them, such
as the British pony breeds and
the Quarter Horse.
The sabino pattern is also a
great imitator, and some of these
horses are nearly perfect mimics
of tobiano or frame overo. When
the sabino pattern is minimally
expressed, the horse usual-
ly has four white socks
and a blaze. Usually
there is some betrayal
of the fact that these
are not the usual
white marks on horses,
due to some ragged edge or long,
narrow extension up the leg.
Some sabinos also have odd white patch-
es on the knee or hock, removed from the
main portion of the lower white mark. A
few sabinos do have a dark foot or two,
although most have four white feet.
Minimally marked sabinos are easily con-
fused with truly nonspotted horses.
In the middle range of expression, sabino
horses are fairly distinctive and are usually
difficult to confuse with other patterns.
Most have white extending from the belly
and have roan and flecked areas in addition
to white areas. However, a few will be near-
ly entirely roan without patches of white.
These could be confused with true roan
horses, although the facial and leg white
usually gives these away, and they do not
have dark heads typical of true roans.
Another extreme is the sabino that is
patched, but not roaned. Sabino horses can
easily be confused with frame overos, espe-
cially if they have one or two dark feet. Most
patched sabinos have smaller, more ragged
patches than is typical of frame overos. In
some cases, it is impossible to distinguish
between horses that are truly sabinos and
the frame overos that also happen to have
white markings on their feet in addition to
the frame overo pattern.
The whitest of the sabinos are nearly or
entirely white. Some retain color only on the
ears and others are white all over. One of
the whiter ranges of expression includes
color on the ears, chest and tail base. These
are the Medicine Hat Paints that were prized
2 • APHA Coat Color Genetics Guide
Frame Overo
Splashed White
Sabino
07CoatColorGenetics 12/14/07 6:51 PM Page 2
While each of the Paint
patterns—tobiano, frame
overo, sabino and
splashed white—can
mark a horse on its
own, many horses sport
combinations of these. When these
patterns combine, the result is a horse
with a pattern that can sometimes be
difficult to classify.
When a mating between a tobiano and an
overo produces an offspring that exhibits
characteristics of both patterns, APHA recog-
nizes the resulting pattern as tovero (pro-
nounced: tow vair´ oh). (It should also be
noted that, while considerably rarer, a cross
between a tobiano and a solid can also pro-
duce a tovero.)
In this instance, the combined patterns pick
up the white from each of their individual com-
ponents. They are then genetically mixed to
create a combination pattern on the horse’s
coat. For instance, a horse with a frame overo
sire might inherit a white framed area on each
of its sides. If the horse had a tobiano dam, it
might inherit a white, blanket-like pattern that
covers its entire back. The result might look
something like the tovero shown on this page,
which is mostly white.
Many of the combinations are called tovero
because most are tobiano plus one of the
other patterns.
Although the word tovero has been a part
of APHA’s vocabulary from the onset of the
registry, it remains to this day somewhat of an
ambiguous term.
Just as there are extremes within the
tobiano and overo coat patterns—from most-
ly dark to mostly white—so are there extremes
within the tovero pattern.
At one end of the spectrum—the mostly dark
one—are those toveros that closely resemble
tobianos except for their face markings, which
show an overo influence. At the opposite end—
the mostly white one—are those toveros whose
only dark pigmentation might appear around
the ears, eyes or chestnuts.
In between those two extremes is the horse
that can be termed the “typical” tovero, dis-
tinguished by the four basic coat characteris-
tics shown below. Typical toveros have:
1. Dark pigmentation around the ears, which
may expand to cover the forehead and/or
eyes.
2. One or both eyes blue.
3. Dark pigmentation around the mouth,
which may extend up the sides of the face
and form spots.
4. Chest spot(s) varying in size. These may
also extend up the neck.
5. Flank spot(s) varying in size. These are
often accompanied by smaller spots that
extend forward across the barrel and up
over the loin.
6. Spots, varying in size, at the base of the tail.
Identifying the tovero pattern is not an easy
task. During the Association’s early years,
some toveros were mistakenly classified as
tobianos or overos. In defense of the people
who misclassified those animals, two points
must be made. First of all, during the registry’s
infancy, the pattern was much rarer than it is
now. There simply weren’t enough toveros
being registered to establish a workable pro-
file of what their physical characteristics were.
Second, it had not yet been firmly estab-
lished how these horses would breed—what
patterns they would produce that would prove
or disprove their classification.
More than 40 years of Association growth
has alleviated both of these conditions, and
the APHA Registration Department now has
the situation well in hand.
Tovero
Typical Tovero Patterns
APHA Coat Color Genetics Guide • 3
by the Native American tribes of
the Great Plains. Most sabinos that
are largely white are very speckled
and roaned, and some can be con-
fused with Appaloosas.
Some sabinos are quite white
and survive, which points to this
being entirely different from the
overo that results in lethal white
foals when homozygous. Sabino,
by itself, is not associated with
lethal white foals.
Splashed White Overo
Splashed white is the least com-
mon of the spotting patterns,
although it is increasing in frequen-
cy as breeders use more splashed
white horses in their breeding pro-
grams.
The pattern usually makes the
horse look as though it has been
dipped in white paint. The legs are
usually white, as are the bottom
portions of the body. The head is
also usually white and the eyes are
frequently blue.
The edges of the white are typi-
cally crisp and clean, with no roan-
ing. Some splashed whites have
dark toplines, but on some the
white crosses the topline.
Recent genetic evidence suggests
that the splashed white pattern is
caused by a dominant gene,
because splashed white foals have
resulted from splashed white to
non-splashed white matings.
Some people have observed that
many splashed white horses are
deaf. This is not much of a problem
if the trainer realizes the limitations
of the horse in question and modi-
fies the training program to meet
the horse’s special needs. Many of
these horses go on to lead normal
and productive lives.
Because no homozygous
splashed white horses have ever
been documented, researchers sus-
pect that this is another gene that
cannot exist in homozygous form.
If this is true, the loss of hearing
probably occurs early in gestation
rather than at term. Because of this,
the best strategy for producing
splashed white horses is to mate
them to horses without the
splashed white pattern.
Tovero
07CoatColorGenetics 12/14/07 6:51 PM Page 3
4 • APHA Coat Color Genetics Guide
Before you begin breeding for color, there
are a few basic genetic concepts you should
understand. Though genetics can seem
daunting at first, by understanding genes
and simple dominance, and knowing how to
use the Punnett Square, any horse owner
can plan their color breeding program with
confidence.
Genes
Genes are the basic units of inheritance.
Genes are linked to form a chromosome
similar to the way pearls are threaded
together to make a strand. Each particular
species has a specific number of chromo-
somes (64 for the horse), and each chro-
mosome has a duplicate mate.
Each gene on the chromosome has a
mate, or allele, in exactly the same place, or
loci, on each of the chromosome’s matched
pair. Basically, each pair of genes codes for
a specific job. A pair of genes can control
something as obvious as whether or not a
cow will have horns, or it may be as subtle
as coding for a specific portion of a bimole-
cular molecule, or controlling the function of
other genes.
During the cell division in which one cell
divides into either two egg or two sperm
cells, only one member of each chromo-
some pair goes into each new cell. This
provides every sperm and egg with only
one copy of each gene. Upon fertilization,
every chromosome, and therefore every
gene, is reunited with its corresponding
mate to create a unique individual.
In coat color genetics, one of the goals is
to identify the possible genes in the parents
and predict the probability of coat colors in
their offspring. To help keep track of the
genes whose function is thought to have
been identified, geneticists assign a letter
of the alphabet to the pair.
Understanding Simple Dominance
Gene interactions can be complex and
confusing. Fortunately, some genes adhere
to a relationship based upon simple domi-
nance. Within this framework, there are two
basic expressions of the same gene—one
dominant, one recessive. The recessive
form of the gene is submissive to the dom-
inant form. The recessive gene is expressed
only when both copies of the gene are in the
recessive form.
Capital letters usually indicate dominant
genes. Lowercase letters indicate recessive
genes. This system is complicated by the
use of superscripts. For example, the dom-
inant form of the gene creating palomino is
CC
cr
. The recessive is referred to as C.
Regardless of the letters used, each
individual obtains one copy of the gene
from each parent. In the system of simple
dominance, this pairing occurs in one of
three ways:
Homozygous dominant—In this instance,
both alleles are in the dominant form, as
indicated by a capital letter, for example,
AA. The color determination is under the
control of the dominant gene, and all off-
spring created from this individual can only
receive a copy of the dominant gene.
Homozygous recessive—Here, both
copies of the allele are in the recessive
form, for example, aa. The color determi-
nation is under the control of the recessive
gene, and in many cases this means there
is no expression.
For example, the recessive form of the
gene for roan (Rn+), palomino (C), gray (g),
tobiano (to) and dun (Dn
nd
) allow the body
coat to be expressed by the dominant gene.
Foals with a homozygous recessive par-
ent will receive one copy of this parent’s
recessive gene.
Heterozygous—One member of the pair
is dominant, while the other is recessive, for
example, Aa. The dominant form is in con-
trol of the expression. Offspring have a 50-
50 chance of inheriting either the dominant
or the recessive gene.
Using the Punnett Square
A Punnett Square is a simple way to pre-
dict the possible genetic combinations from
the mating of two individuals. To use this tool,
first draw a square. Across the top, list the
gene combination of the stallion. Down the
left side, list the gene combination of the
mare. Then, bring one v
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