¶ Pinto Patterns
¶ Overview
There are 4 pinto patterns:
- Tobiano
- Frame Overo
- Sabino/Dominant White
- Splashed White
Each is caused by a single gene, but, similar to regular white markings, pinto patterns can be affected by other genes to make more or less white (i.e. ‘loudness’). You can read more below!
¶ The Patterns
¶ Tobiano
Tobiano is caused by a part of chromosome 3 that was inverted. Yes, that’s right, a piece of chromosome 3 was taken out and accidentally turned around, before getting pasted back into the chromosome. We should specify that this happened naturally. Neat, huh? This inversion was pretty large, and flipped around several genes. How exactly this inversion causes the tobiano patterning is unknown, but the inversion can easily be detected, and when it is, you get tobiano.
Tobiano usually causes horses to have white markings on all four legs, and white will often cross the horse's topline/back too. Tobiano does not appear to cause face markings or blue eyes though, and the gene acts in a complete dominant matter. That is, a TO/TO horse and a TO/n horse will be indistinguishable.
¶ Frame Overo/Lethal White Overo
The frame overo pattern is caused by a mutation in the EDNRB gene. Frame overo horses usually have at least a little white on the face, but often have blazes or bald faces, and sometimes even blue eyes. They will also usually have some white on their body, but it won't cross their back, producing white splotches that look like they have been ‘framed’ on the horse's sides. As for the legs, whether or not frame directly causes white on the legs is uncertain in real life, and frame horses usually have at least one solid leg. Because of this, we decided to make it so that frame in Legacy does not cause leg markings. You can still get leg markings with the regular white marking genes though!
There is one very important thing to know about frame overo though. You do NOT want to breed for homozygous frame horses. Homozygous foals will have severe intestinal tract problems, which will lead to them dying soon after birth. That means breeding a heterozygous frame horse with another gives you a 25% chance risk of producing a lethal white overo foal!
¶ Sabino/Dominant White
Both Sabino and Dominant White are caused by the same gene, known as KIT. KIT is highly polymorphic in horses, meaning it has numerous alleles. Last we checked, there were almost 30 alleles in real life! But, most are extremely rare (only in one breed, or a few horses), and all create a range of sabinos and dominant white patterns. Because these rarer alleles are not well characterized (i.e., we don’t have a lot of examples to look at), and most appear to create overlapping phenotypes, we did not include all ~30 alleles in Legacy.
For the game, we selected more common alleles that function ‘differently’. That is, they produce different ranges of white on the KIT pattern ‘loudness’ scale. The selected alleles are SAB1, W1, W10, W14 and W20. Horses with KIT mutations will have patterns ranging from very discrete, normal looking face and leg markings, to face and leg markings with white patches (usually on the flank), to completely white horses. KIT does not cause blue eyes though.
Because KIT is so complicated, there are actually eight loudness levels in the game, rather than five like the other pinto patterns! You can read more about loudness below. We won't tell you what ranges each allele produces though, but they all behave in an incomplete dominant manner.
While KIT produces a lot of beautiful patterns, there are two down sides to KIT mutations. The first is that KIT mutations decrease stallion fertility (you can read more about this in the fertility/reproduction sections). The second is that some alleles are lethal when homozygous, or when mixed with another mutant KIT allele. Because there are so many alleles and combinations of alleles in real life, we don't know all lethal genotypes, but for the game the following are lethal:
W1/W1
W1/SAB1
W1/W20
W1/W14
W1/W10
So, avoid pairing horses together that could give you the above genotypes!
¶ Splashed White
Splashed White 1 (SW1) is caused by a mutation in the MITF gene. This SW1 allele causes a white pattern that looks like the horse has been ‘dipped’ in white, although some splashes are so subtle the horse will just have ‘normal’ looking face and leg markings. They will often have blue eyes as well. SW1 acts in an incomplete dominant manner, meaning SW1/SW1 horses are usually distinguishable from SW1/n.
Side note: SW1 isn’t the only MITF allele which causes splashed white though; there are also SW3, SW5 and SW6 alleles. Where are SW2 and SW4? They are actually alleles of a different gene, PAX3. For Legacy though, we will only be including the MITF gene, and just SW1. Too little is known about the other SW alleles right now, and from what we do know, they appear to make the exact same phenotype as SW1. We don’t see the point in ‘bulking up’ the code with genes that do the same thing. Also, there is some speculation that some of these newer SW alleles may be lethal in their homozygous state, adding to our hesitancy to include them.
¶ Pattern ‘Loudness’
You can also breed for different levels of white "loudness" (more or less white) in the above pinto patterns. For each pattern, there are 5* levels controlled by genetics, but within each level there will be random variation that you cannot breed for. KIT (sabino and dominant white) is the only exception, where there are 8 levels of pattern loudness controlled by genetics.
I'm afraid we can't tell you too much about what genes affect pattern loudness, but, just like in real life, pinto genes which show incomplete dominance (sabino and splashed white), will also affect pattern loudness in Legacy too. Meaning, SB1/SB1 horses will usually have more white than SB1/n horses, for one example. But there will still be variation even within SB1/n or SB1/SB1 horses. Aside from this, there are 4 other genes affecting pinto pattern loudness.
Below is an example of the five levels of frame overo loudness.
