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Known or under-investigation
dilutions:
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Dilution means less concentration; like milk
dilutes the color of coffee, a dilution gene causes a lighter
hair color.
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Dilution genes contain instructions to the cells producing pigment (color) in
the horse's hair and skin to "spread the pigment thinner", or to
"dilute" the pigment.
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Dilution genes do not
"switch off" pigment (color), as white-spotting, gray, and Appaloosa
genes do in horses,
or as albino genes do in mice.
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This picture, taken by the webmaster
in 2006, is of a black-based
(brown)
champagne-dilution
(sable)
foal near Bend, Oregon. Because the black color is
diluted, the coat, mane & tail are not black, but a very
interesting, lighter color. The eyes are blue, and
the skin is pink, all over. As the foal ages, its
eyes will turn tan, and its skin will develop abundant
dark freckles. The skin does have some pigment in
it, and is a different shade of pink then the
pigment-free skin under pure-white markings.
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NEW TERMS! Some dilution genes
are dominant, but some are incompletely
dominant, and some are incompletely
recessive.
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Incomplete dominant genes :
expressed partially when one is present, more when
double
(HOMOzygous)
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Incomplete recessive genes :
expressed minimally when one is present, completely when
double
(HOMOzygous)
To differentiate them from
incomplete dominant or incomplete recessive genes,
sometimes "regular" dominant or recessive genes
are called "simple dominant" and "simple recessive" genes.
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This picture, also taken by the
webmaster in 2006, is of a "teen-aged" Iberian filly of
the pearl-cream dilution in Acton, California. She
was born with pink skin and blue eyes, and her skin was
already developing freckles typical of the pearl
dilution -- usually somewhat muted compared to champagne
freckling. Her eyes eventually turned more
of a greenish color.
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The currently
known dilution genes are: |
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The cream gene is abbreviated "Cr" in genetic
symbols. The gene for absence of cream is abbreviated "cr".
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The cream gene is an
INCOMPLETE DOMINANT gene. This means that if one
gene is present, it will be expressed moderately, and if two
copies are present, it will be expressed in a more extreme
manner. 
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One cream gene will lighten the base colors to
the single-cream colors,
such as palomino or buckskin (illustrated) or brown buckskin or smoky
black.
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  Two
cream genes will lighten the base colors to
the double-cream colors,
such as cremello or perlino (illustrated) or brown cream or smoky cream.
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 The Dun gene is abbreviated "D" (or
"Dn") in genetic symbols. The gene for absence of Dun is
abbreviated "d" (or
dn).
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The Dun gene is believed to be a (SIMPLE) DOMINANT gene. This means
that if one gene is present it will manifest fully, and if two are
present it manifests no differently than with one.
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The Dun gene lightens the body color and leaves stripes
of the original color along the back and on the upper legs,
most of the mane & tail, and other specific places.
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this means that dun
on chestnut will result in a washed-out-red body
color with chestnut colored stripes;
on bay will result in a tan body color with dark red
points and stripes (sometimes striping on a bay dun can
look black; presumably that horse would have been a
sooty bay without
the dun gene); on black
will result in a dove gray to purplish to olive brown body color with
black points and striping; on brown,
dun looks much like it does on black, and a DNA test is
usually needed to prove the difference.
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FOR MORE ON DUN, see
this web site's dun section; also
DunGenes.org, also by
this webmaster.
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The Silver gene is abbreviated "Z" in genetic
symbols. The gene for absence of Silver is abbreviated
"z".
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The Silver gene is a SIMPLE DOMINANT gene. This
means that if one gene is present it will manifest fully, and if two are
present it manifests no differently than with one.
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The Silver gene ONLY AFFECTS BLACK PIGMENT.
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Silver "super-dilutes" the mane & tail of a horse
with black pigment to a flaxen or silvery color.
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Silver dilutes the black pigment on the
body to a chocolate-brown shade (illustrated).
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Silver does not dilute the red pigment of a
bay based horse, leaving a red body with flaxen mane & tail
and chocolate-brown lower legs (where the black is diluted).
(not illustrated)
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 The Champagne gene is abbreviated "Ch" in
genetic symbols. The gene for absence of Champagne is abbreviated
"ch".
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The Champagne gene is a SIMPLE DOMINANT gene. This
means that if one gene is present it will manifest fully, and if two are
present it manifests no differently than with one.
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The Champagne gene lightens the hair, skin
and eye color (illustrated on bay).
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Champagne foals are born with pink skin and blue
eyes; the pink skin color usually deepens and always develops dark freckles,
and the eye color turns to amber or light brown.
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 The
pearl gene is abbreviated prl.
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Pearl behaves as though it is an allele
(mutation) of cream.
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It is an incomplete recessive gene; one pearl gene is
minimally expressed, if at all,
when no cream is present.
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It reacts with cream to form a type of
double-dilute: a cream pearl, with pink skin and muted
freckles.
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A horse with two pearl genes will be a
diluted color, with pink skin and muted freckles
(illustrated on black).
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It was once believed by some that flaxen was
a simple recessive gene.
However, we now have evidence that two flaxen chestnuts do
not always produce a flaxen foal. So...
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At the time of this writing, the mechanism
by which flaxen is inherited is unknown.
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Flaxen only affects red pigment in manes
and tails of red-based horses.
Besides these six currently-known dilution genes, one of which
(flaxen) is far from understood, there are at least two other
possible dilutions under investigation:
light black and
mushroom. These are
extremely rare, the former occurring mostly in one family of Arabian
horses, and the latter almost exclusively in one "family" of English
Shetland ponies. To follow or join in these investigations,
click either of these links:
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