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This notice is not meant as a rebuke or to put down players who are new to the game and to the world of scientific horse color genetics. It is made as a public service to shine light on the contrasting terms that have commonly been used in the horse world to refer to certain patterns as opposed to the terminology here in the game, which is based on the identification of various gene mutations discovered through research

Since a major focus of this game is education on the current knowledge about horse color genetics, we use a slightly different vocabulary when referring to various genes that cause white markings on a horse than you may be used to. Because of the continuing advance in the identifying of individual genes and their effects, we are able to be more specific in naming certain patterns than in the days when the patterns were named based only on their appearance.

Ammit also keeps up with current research and adjusts the game to reflect new discoveries. I hope this post will help you know what we are talking about when we use names that are not familiar to you.

Overo
This term was originally applied to any spotted horse that was not Tobiano and that had its pigmented hairs confined to its top line and its belly. The white spots would have jagged edges and be concentrated along the sides of the barrel or the middle of the neck.

The gene that causes this pattern to form was identified early, and is now referred to as Frame. It's abbreviation on color test results is Olw, for Overo-lethal white. It has this name because foals that are homozygous for Frame are born solid white and with an incomplete digestive system and quickly die from impaction colic.

We do not use the term "Overo" in the game. (You will also never see Paint, Pinto, Piebald, Skewbald or Pintaloosa in the color name of a gene tested horse.)

Frame works together with certain other genes that cause white spots of various sorts. Many of them have been identified and given names.

Note that horses can carry the Frame gene without having any genes that cause white spotting. If two horses that don't have white spots but do carry Frame are bred together, the result is still a dead foal if it inherits Frame from both parents.

Genes that cause white spots and are influenced by Frame
Most of the genes that cause white spots are fairly obviously influenced by Frame, especially if the spotting is widespread or produces large spots.

Tobiano is one exception. A Tobiano horse that also carries Frame may have smaller white spots and pigmented hairs that extend farther down the leg than they would have without the Frame. The effect of Frame on Tobiano is subtle and can be very hard to spot. Roan does not appear to be influenced by Frame at all.

Splash is a pattern of white that extends up through the legs onto the belly. The white may reach fairly high up the barrel. It also appears on the face starting with the muzzle and reaching as far as above the eyes.

I believe there are now three identified mutations that cause this pattern. Two of them, Splash 1 (Sps) and Splash 3 (Sps3) are separate mutations of the same gene, known as MITF. Splash 2 is a mutation of an entirely separate gene PAX3.

Depending on how much white there is, you may or may not be able to spot any effect of Frame when the Splash is heterozygous. Frame plus homozygous Splash (Sps 1)is very easily identified.

Splash 2 and Splash 3 are homozygous lethal (kill the foal when it gets these genes from both parents). Splash 2 and Splash 3 combined also result in a dead foal. Splash 1 can safely be combined with itself, however, as well as with either Splash 2 or Splash 3.

Kit Mutations

The Kit gene is a long one, and over the years since horses first evolved, has developed many mutations that can cause white spots or, in the case of Roan, individual white hairs scattered throughout the coat. Tobiano, referred to above, is also one of the Kit mutations.

There are two other kinds of Kit mutations. Some of them break the gene so badly that they are homozygous lethal. These mutations used to be referred to as Dominant White. An embryo that received any two of these genes from its parents would die early in its development in the uterus and be reabsorbed into the mare's body. These mutations used to be referred to as White followed by a number.

There are other mutations of the Kit gene that cause similar white spotting patterns that are not homozygous lethal, although some of them do interact with certain Dominant White genes to produce a dead foal. These mutations have been referred to as Sabino in the past.

In agreement with the current practice in horse color genetics, horses with both of these groups of Kit mutations will soon be referred to in the game as White Spotted ..., with the exact mutation referred to in the gene test results as Kit^W + number. So you might see a horse whose color is named White Spotted Silver Bay Dun Splash Tobiano Appaloosa Frame.

An exception to this last rule, as Ammit has just announced, will be Sabino 1, which will still appear as Kit^Sb.