For the last hundred years or so, domestic breeding of horses has been based on confirmation and performance ability, but also on color. When it comes to color we could make a very educated guess, but with the current research into Equine color genetics, the "guessing" has been taken out of the equation. The great thing is you don't have to have a Ph.D to understand color genetics in horses. Equine colors are fairly simple in the world of genetics.
Basic horse coat colors are chestnut/sorrel, bay, and black. All other equine coat colors are derived from these three bases. The three base colors are controlled by two genes, The Extension Gene which controls black and non-black, and the Agouti Gene which controls locations of black pigment. There are approximately 10 other genes that modify coat color in horses.
In this article I will look at the Extension and Agouti Gene, in the next article we will look at the modifier genes.
Genetics Terminology used in this article:
allele - each gene has two forms called alleles, the alleles can be the same (homozygous) or different (heterozygous)
homozygous - both alleles present are the same. i.e EE or aa
heterozygous - different forms of the allele are present. i.e Ee or Aa
Extension Gene EE, Ee, ee
The Extension gene (E) controls black and non-black.
(ee) Chestnut or sorrel horses are homozygous recessive (ee) for the extension factor. We call this the red gene. Horses born without black pigment on the body carry this genotype. Horses that have this gene and modifiers are palomino, red dun, cremello, white, or gray. This horse will produce red and bay foals.
(Ee) Horses that are heterzygous (Ee) are generally bay, black, or brown, depending on the Agouti gene. Horses with this genetic make-up rely on the Agouti gene to distribute the black pigment either at the points or over the whole body. This horse can produce red, black, or bay foals. If a horse carries this heterozygous gene and modifiers their coat will be buckskin, zebra dun, grullo, perlino, gray, or white.
(EE) Horses that are homozygous dominant for the Extension Factor (EE) are black. The red factor is not detected. In this case the Agouti gene does not effect the distribution of black on the body. This horse cannot produce a chestnut or sorrel foal, because they will always provide a dominate gene allele (E). If modifiers are present this horse will be buckskin, zebra dun, grullo, perlino, gray or white.
The Agouti Gene (A) controls the distribution of black on the body.
(AA and Aa) Homozygous dominant and heterzygous (AA, Aa) horses have black on the body at the points, ears, legs, mane, tail. This genotype includes bays, buckskin, zebra dun, and grullo.
(aa) Homozygous recessive horses (aa) will have black uniformly over the body, this will be the "true" black horse. This horse will have the genotype of EE/aa. This horse will also produce only black foals and if breed to other horses with this genotype, will produce a black foal each time.
So this year as you prepare to breed your mares and stallions, if you want to know what color your foals will be use the Equine Color Calculator, and get the 4 possible colors of your babies! This particular calculator works on solid and paint horses, unfortunately it does not include Appaloosas.
(If you know of one that does, please email the link to Lydiabagley@aggienetwork.com)
Comments