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Horse of a Different Color Genetics

Updated on June 3, 2014

Horse Coat Colors

Horse coat color genetics is a science that anyone can learn with a little help. Here you will learn a few new words and what they mean concerning horse color genetics. By the end of this hub you should be able to identify the basic coat colors and how they are affected by other genes. Let's get started!

Basic Coat Colors

The Base Colors
The Base Colors | Source

UC Davis Genetic Testing

UC Davis offers testing for many of the genetic markers for colors such as dun, perlino, lethal white overo, palomino, appaloosa, and many more.

DNA, Genes & Alleles

Everything is made up of DNA, you are too!

  • DNA is a microscopic strand that has all the information to make you who you are. It details everything from the color and texture of your hair at the top of your head, down to the toenails on your toes.
  • Each piece of information in the DNA is called a gene.
  • Hair color genes, along with other genes, can have an alternate state and that is called an allele.

Geneticists (scientists that study genes) have narrowed down the genes that make up the color of a horses coat! What they have found is there is a gene they named the Extension gene that is responsible for the red and black pigment. The extension gene has two alternative states. They are the allele E representing black pigment and the allele e for red pigment. The capital E tells us that the gene is dominant. The lowercase e tells us it is recessive or hidden.

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It Takes Two to Make One

Most of us are aware that it takes a mommy horse (mare) and a daddy horse (stud or sire) to make a baby horse (foal). The mare and the stud each contribute half of their DNA. When we refer to the DNA of a horses coat color we write it with two letters, one representing each parent. For example, if the horse has the Extension gene from the mare, and one from the stud, it would be written: E/E.

The Extension gene controls the production of black and red in the coat. The agouti gene effects the way the black is distributed on the body or whether it is only on the points. The points include the nose, mane, tail and legs, which is a bay colored horse.

The two genes producing black and red coat color are the base for the four basic coat colors. They are black, bay, red (chestnut) and brown. All of the other coat colors begin with one of these basic colors and builds on it with various genes.

Hetero - or Homo - zygous

Homozygous and heterozygous refer to the two letters in the color code.

  • Homozygous means the letters are identical alleles. Example: E/E, e/e, Ccr/Ccr
  • Heterozygous means the alleles are not similar. Example: E/e, A/e, Ccr/e

Extenders and Alleles

If you have a dominant E from the mare and a dominant E from the stud, you have E/E. This is true black. This black will never fade (see photo). Because the alleles E/E are exactly the same. The horse is said to be homozygous.

This is a True Black (Notice the coat has a blue hue to it)
This is a True Black (Notice the coat has a blue hue to it) | Source

Fading Black or Bay

If you have a dominant E from one parent and a recessive e from the other you get E/e. This horse will be either bay or black. The black in this allele combination will fade if he is in the sunlight too much. The E will extend the black color all over the coat, but the recessive e (remember its red) will not allow the black into the core of the hair. When a black horse with the E/e gene is outside a lot, he will fade and you will see a red tinge to his coat (see photo).

E/e  Fading Black (Notice the red hue)
E/e Fading Black (Notice the red hue) | Source

Basic Coat Color Genetic Table

Coat Color
Homo or Hetero
True Black. Will never fade.
Homozygous for black (EE)
Black, possibly bay. This black will fade.
Sorrel or Chestnut
Homozygous for red (ee)

Coat Color Calculator

There is a cool Coat Color Calculator here. From the drop-down menu's you enter the color or the stud and dam and the pattern. The next screen asks more in depth information about the genetic code IE: Ee, aa, Aa, etc. of the stud and dam. When you click enter a screen with a complete breakdown is presented with the results for the offspring.

There's So Much More

This is just an introduction to horse coat color genetics. There is more exciting factors and colors and colors that make patterns!! If you understood this hub then you have a good grasp of he basics in horse coat color genetics.

To read more on coat color genetics try:


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