While much is still to be learned about the genetics behind appaloosa coat patterns (blankets, leopards, snowcaps, few spots, varnish, etc.), 2 genes have been identified that affect the physical characteristics of these types of patterns. This post is meant to set some "guidelines" for myself to use when pedigreeing horses with appaloosa patterning. While the genotypes and corresponding phenotypes listed below may not be entirely accurate, they are guided by the information currently available from the links at the bottom of this post. Please note that I use the term "appaloosa spotting" in place of "leopard complex spotting" as to avoid confusion between the leopard complex gene and the leopard spotting pattern. Many breeds display appaloosa spotting patterns in their gene pools so this post can be used as a reference for a variety of breeds, not just Appaloosas. LP - Leopard ComplexThe leopard complex gene has been known for some time now (at least as long as I've participated in pedigree assignment). This gene is the "on/off" switch for appaloosa spotting and is also the reason why appaloosa spotting can "skip" a generation on occasion. With one dominant allele (Lp), a horse will display some type of appaloosa spotting. Whether that spotting is simple varnish, leopard, blanket, or some other spotting depends on additional modifiers (kind of like cream and champagne, which are base coat modifiers, more often called dilute genes). A horse that is heterozygous for leopard complex (nLp) will often display more "holes" in the white patches (or spots) than a horse that is homozygous for leopard complex (LpLp). I use this knowledge later differentiate snowcaps from spotted blankets and other similar comparisons. ModifiersWithout any modifiers, a horse with the leopard complex gene will just be varnish roan. Additional modifiers are what make distinct boundaries for the leopard complex gene, such as leopard and blanket. One modifier has been identified, PATN1, which is assumed to create leopards and few spot appaloosas. An additional modifier is theorized to exist for blankets and snowcaps. Similar to leopard complex, PATN1 also controls the amount of "holes" present in the horse's coat. A horse heterozygous for both leopard complex and PATN1 could look like a semi-leopard or a leopard with large spots and likely little varnishing on the face and legs. A horse who is heterozygous for leopard complex but homozygous for PATN1 will likely be a full leopard with varnishing and spots on the legs and face. A horse who is homozygous for just leopard complex and heterozygous for PATN1 will probably look like a few spot appaloosa; and a horse who is homozygous for both leopard complex and PATN1 will likely be entirely white. Any dark spots these horses have will probably be heavily mottled or varnished out. This means that you'd probably have to genetic test a horse (unless you know the parents pattern) to find out if they are appaloosa or dominant white since both can look similar. Breakdown of the GenotypesBelow are a bunch of pictures with possible genotypes listed below them. These genotypes are not confirmed, but I plan to use this as a reference for assigning genetic profiles to my models until further information is known. Below are some charts that might help distinguish nLp horses from LpLp horses. "The charts above deliberately do not show varnishing which changes year on year but in each of these cases the horse will also show varnish roan characteristics and “varnish out” to varying degrees with age. " Final ThoughtsFor model horse purposes, I will follow these "guidelines" until more information is available. nLp horses will have body spots in addition to "normal" appaloosa characteristics (skin mottling, varnishing, striped hooves, etc.). LpLp horses will have no or almost no body spots, but still have normal appaloosa characteristics. A horse who carries one copy of the PATN1 mutation will have the white on their body passing the barrel but not fully covering the face and/or legs. A horse with two copies of the PATN1 mutation will have white that extends across the whole body. Whether or not there are dark spots within these white patches depends on the presence of the Lp gene. Until more information is available, all horses with blankets or snowcaps that do not pass mid-barrel will simply be listed as having an unknown "blanket modifier." As always, if you have any questions or want to pick my brain a little, don't hesitate to comment here or email me. If you are more knowledgeable on this topic and have more to add or corrections to make, please let me know so I can update this post! I love learning about this stuff and I'm sure I missed something. You can find my references below. Thanks for reading, Reagan References
https://good-horse.com/genetics-evolution/introduction-appaloosa-patterns-genetics/ https://vgl.ucdavis.edu/test/appaloosa-pattern-1#:~:text=A%20dominant%20mutation%20%28PATN1%29%20was%20identified%20that%20is,the%20range%20is%20generally%20from%200-40%25%20at%20birth.
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