HOME | DD

Description
You may use this as a reference for realistic TB colors and patterns.
You may share this with friends, as long as Prongy is linked to.
You may not upload this to your own account or reproduce it in any way.
You may not claim you played any part in the creation of this resource.

Read below for additional information and answered questions.

Why did you remove At and recombine brown with bay?
The test for the supposed agouti mutation was pulled shortly before the lab closed its doors. Test results were inconsistent, such as black horses tested as E/- aa at other labs like UC Davis coming back as brown or bay carrying brown at the brown-testing lab. The man in charge of this lab openly admitted to the test being wrong while being contradictory and claiming that their research (which was done on mice) was correct. Though they constantly swapped between calling it an allele and a marker, which are two completely different things in genetics. Reputable labs have completely mapped the agouti locus and it has only two alleles, A and a, making it impossible for there to be a third allele on agouti causing brown. It is currently unknown if and what other factors exist that cause the brown phenotype in bay horses.

Why did you take sabino out of the white patterns?
Sabino as a testable pattern (sabino 1, Sb1) does not exist in the Thoroughbred genotype. No Thoroughbred to date has come back positive for the sabino 1 mutation on KIT. The word "sabino" is often erroneously used by laymen to refer to any sabino-like white patterning as well as any white face and leg markings in general, which is simply incorrect. The sabino mutation was mapped to KIT and named before the discovery of the mutations they started calling dominant white (since renamed to white spotting, since the word "dominant" was used in reference to a thought that the white patterning always dominated over the body color, which was proven incorrect and thus the mutations renamed). It is personal theory that sabino 1 and white spotting are likely closely-related mutations, all being on KIT and having similar phenotypes, and just follow different naming conventions.

Why is dun not included?
Thoroughbreds do not have the dominant dun gene that causes dilution and primitive markings. It is possible, but not confirmed as I have yet to see tests on a Thoroughbred, that they may have the not-dun 1 gene on the dun locus, which does not dilute and often adds primitive markings (the not-dun 2 gene would be our previously-known d - so there are D, nd1, and nd2). Thoroughbreds, along with many other breeds, may also have false dorsal stripes from an unknown cause such as sooty or simply just coat color variation.

Why is tobiano not included?
Like dun, Thoroughbreds do not have the tobiano mutation on KIT. For a minute, this confused me since the American Paint Horse breed has the pattern when neither of the major foundation breeds have it. I discovered when I went back through tested tobiano Paint pedigrees, that the tobiano mutation in the breed originated from grade horses bred to Thoroughbreds and Quarter Horses.

Why is roan not included?
Roan does not naturally occur in the Thoroughbred breed. The only known true roan Thoroughbreds are from a single bloodline out of New Zealand, originating from the oddly-colored stallion Catch A Bird. Neither of Catch a Bird's parents had any white patterning, so he wasn't roan himself as roans must have one roan parent. The Jockey Club only does live cover and DNA tests to confirm parentage before registering foals, so the roan popping up is definitely due to an extremely rare mutation that is unlikely to happen again in the next 200 years. There are many theories around this, but nothing has been confirmed. I personally believe that it is the result of a skewed rabicano gene mutating into roan in the foals, seeing as Catch a Bird had obvious rabicano traits as do some of his roan progeny.

Chart © Prongy
Horse template © Rosenhill

Description
You may use this as a reference for realistic TB colors and patterns.
You may share this with friends, as long as Prongy is linked to.
You may not upload this to your own account or reproduce it in any way.
You may not claim you played any part in the creation of this resource.

Read below for additional information and answered questions.

Why did you remove At and recombine brown with bay?
The test for the supposed agouti mutation was pulled shortly before the lab closed its doors. Test results were inconsistent, such as black horses tested as E/- aa at other labs like UC Davis coming back as brown or bay carrying brown at the brown-testing lab. The man in charge of this lab openly admitted to the test being wrong while being contradictory and claiming that their research (which was done on mice) was correct. Though they constantly swapped between calling it an allele and a marker, which are two completely different things in genetics. Reputable labs have completely mapped the agouti locus and it has only two alleles, A and a, making it impossible for there to be a third allele on agouti causing brown. It is currently unknown if and what other factors exist that cause the brown phenotype in bay horses.

Why did you take sabino out of the white patterns?
Sabino as a testable pattern (sabino 1, Sb1) does not exist in the Thoroughbred genotype. No Thoroughbred to date has come back positive for the sabino 1 mutation on KIT. The word "sabino" is often erroneously used by laymen to refer to any sabino-like white patterning as well as any white face and leg markings in general, which is simply incorrect. The sabino mutation was mapped to KIT and named before the discovery of the mutations they started calling dominant white (since renamed to white spotting, since the word "dominant" was used in reference to a thought that the white patterning always dominated over the body color, which was proven incorrect and thus the mutations renamed). It is personal theory that sabino 1 and white spotting are likely closely-related mutations, all being on KIT and having similar phenotypes, and just follow different naming conventions.

Why is dun not included?
Thoroughbreds do not have the dominant dun gene that causes dilution and primitive markings. It is possible, but not confirmed as I have yet to see tests on a Thoroughbred, that they may have the not-dun 1 gene on the dun locus, which does not dilute and often adds primitive markings (the not-dun 2 gene would be our previously-known d - so there are D, nd1, and nd2). Thoroughbreds, along with many other breeds, may also have false dorsal stripes from an unknown cause such as sooty or simply just coat color variation.

Why is tobiano not included?
Like dun, Thoroughbreds do not have the tobiano mutation on KIT. For a minute, this confused me since the American Paint Horse breed has the pattern when neither of the major foundation breeds have it. I discovered when I went back through tested tobiano Paint pedigrees, that the tobiano mutation in the breed originated from grade horses bred to Thoroughbreds and Quarter Horses.

Why is roan not included?
Roan does not naturally occur in the Thoroughbred breed. The only known true roan Thoroughbreds are from a single bloodline out of New Zealand, originating from the oddly-colored stallion Catch A Bird. Neither of Catch a Bird's parents had any white patterning, so he wasn't roan himself as roans must have one roan parent. The Jockey Club only does live cover and DNA tests to confirm parentage before registering foals, so the roan popping up is definitely due to an extremely rare mutation that is unlikely to happen again in the next 200 years. There are many theories around this, but nothing has been confirmed. I personally believe that it is the result of a skewed rabicano gene mutating into roan in the foals, seeing as Catch a Bird had obvious rabicano traits as do some of his roan progeny.

Chart © Prongy
Horse template © Rosenhill