Post by High Point Stable on Aug 10, 2012 12:54:30 GMT -5
Since I get many PMs about genetics-related things, I decided to put up a thread about it so that it's public knowledge and people can ask their questions here and everyone else can learn from it
UNDER CONTRUCTION
Introduction
UNDER CONTRUCTION
Introduction
Genetics. There is a certain misconception, neither common nor uncommon, that the science behind genetics and genetic inheritance in reference to horse coat colors is complex and difficult to understand. It is not. One does not need to be a thermonuclear physicist to understand how genes are passed along and interact with each other. It is really quite simple as long as someone isn't trying to teach you about what exactly DNA is and what it's made of and its structure and all that kind of crap. That stuff is not relevant to our needs on Equus. I just want to teach you about colors. Judging by the number of PMs I get, I'm guessing some of you want to learn about them.
Let's start with useful terms you'll want to know:
Gene -
Allele -
Dominant -
Recessive -
Incomplete Dominant -
Codominant -
Heterozygous -
Homozygous -
BASE COLORS
A chestnut horse and a black horse. What do they have in common?
They are the two purest colors a horse can be. All other colors in the wide and varied spectrum of equine coats are the result of other genes working on either of these two. All of your favorite colors - palomino, amber champagne, blue roan, even bay and gray - are, at their very bottom 'layer,' either chestnut (henceforth referred to as 'red') or black.
Black is dominant over red. Wherever a black gene is present, the black base will show; a horse with one copy of black and one copy of red will always be black-based. A horse with two copies of black will also obviously be black, but a horse with two copies of the recessive red will, in fact, be red. We refer to a red gene as a lower case 'e' when speaking in genes, while black is represented by the upper case 'E'.
A chestnut horse will thus be ee, while a homozygous black horse, or one who will never produce red-based offspring, is EE. A heterozygous horse, Ee, is black-based but can produce red when bred to another heterozygous or red-based horse.
AGOUTI
pic of a seal brown, bay, and wild bay
pic of a seal brown, bay, and wild bay
Agouti is very unique in that it has more than one expression. It has three, in fact. Regardless of the expression, Agouti works only on black hair and it works by lightening the hair in certain areas, typically to red or brown in the absence of other genes. Because it does not work on red hair, it will not be visible on a horse that is red-based: a chestnut horse can carry an Agouti gene, but without genetic testing, you won't know for sure.
GRAY
why gray is not white, Gg GG
CREAM AND PEARL
palomino buckskin smoky black cremello perlino smoky cream, Crcr CrCr
pearl dilutes - prl
CHAMPAGE
amber classic blah blah blah Chch ChCh
DUN
red bay grullo Dd DD
SILVER
and why it's not the same as flaxen Zz ZZ
FLAXEN
the blonde mane woo ff
ROAN
dark head and legs RnRn Rnrn
RABICANO
it's not roan, people! RbRb Rbrb
SABINO
Sabino is the most common of all the pinto patterns. It puts white on the legs, face, and underbelly of the horse first and slowly works its way up and in. Very common indicators of sabino include leg markings above the knees and hocks, facial white extending to the lower lip, and belly spots, but other indicators include disconnected patches of white on the legs, throat, and white hairs scattered throughout the coat that are not related to rabicano, roan, or gray. Sabino does not cause blue eyes even in its maximum, homozygous form. Sabino is also characterized by jagged edges and 'roaning' where the white and the color meet. It is suspected that there are several sabino genes, but the only one that has been confirmed so far is Sb1, which surprisingly does not exist in some breeds that were thought to commonly have it - thoroughbreds, Arabians, and Clydesdales, for example.
FRAME OVERO
Frame overo is the gene that causes the lethal white horse. It is a color pattern that expresses itself by putting white on the body of the horse rather than on the legs. Face white is typical of a frame overo, but leg white tends to be minimal or nonexistant. The white from frame overo does not cross over the back, under the belly, or across the chest of the horse except when in combination with other patterns or in very extremely expressed cases. Frame over tends to have coarse edges on the white as well, but not roaned like sabino; the white is sharp, but not smooth. Frame overo does sometimes cause blue eyes especially when the face white touches or covers one or both eyes.
All frame overos are heterozygous. Frame is lethal in its homozygous form. A homozygous foal will typically be born alive and will either be solid white or almost solid white with few hairs. The foal's digestive track is not completely developed and so it cannot pass mecronium or digest its mothers milk, resulting in an agonizing death within only a few days of birth. It is therefore highly inadvisable to breed frame to frame as the odds of getting a frame foal are exactly the same as they are when breeding frame to solid.
TOBIANO
Tt TT
SPLASH WHITE
more on incomplete dominants, Sw1 Sw2 Sw3
DOMINANT WHITE
it's a genetic mutation dudes Ww
YE OLDE SPOTTED HORSE
the leopard complex; varnish, leopard, fewspot, blanket, snowcap. LP PATN1 PATN2
FAQ
BREEDS AND COLORS
Here are a list of (some) breeds and the colors they come in. I will not do crosses like anglo-arabian, appendix quarter horse, morab, pintabian, etc.
Arabian
Black
Seal Brown - rare
Bay
Wild Bay - rare
Chestnut
---Flaxen
Gray
Rabicano - uncommon
Dominant White - rare
Splash White - very rare
Sabino(?) - rare
SB1 NOT FOUND IN ARABIANS
Thoroughbred
Black - rare
Seal Brown
Bay
Wild Bay - very rare
Chestnut
----Flaxen - rare
Gray
Roan - very extremely rare
Cream Dilutes - rare
Rabicano - rare
Dominant White - rare
Frame Overo - rare
Splash White - rare
Sabino(?) - uncommon
SB1 NOT FOUND IN THOROUGHBREDS
Standardbred
Black
Seal Brown
Bay
Chestnut - uncommon
----Flaxen - rare
Gray - rare
Roan - very, very rare
Dominant White - extremely rare
Tobiano - extremely rare
Sabino(?) - extremely rare
Splash White - suspected to exist but be extremely, super rare
SB1 NOT FOUND IN STANDARDBREDS
Quarter Horse/Paint
Morgan
Saddlebred
AMH
etc[/center]