W21 is one of the many different variations of white spotting.
¶ Phenotype
W21 is present in Icelandic Horses, the Icelandic word for the pattern is ýruskjóttur. Horses with W21 have belly spots, large face and leg markings, and blue-coloured eyes are possible too. Typical white spotting characteristics are also present: the white patches often have irregular, jagged edges and white ticking is usually present in the pigmented areas.
W21 affects any base colour, but the presence of dilutions or grey may make the white pattern harder to see. When the pattern is very expressive, W21 may make it difficult to recognise the underlying colour of the horse without genetic testing.
| W21 - Icelandic Horse |
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¶ Genotype
W21 is a white spotting mutation on the KIT locus (a deletion at exon 17). No horses homozygous for W21 have been recorded, therefore, it is suspected to be embryonic lethal in real life. In Horse Reality, breeding two horses together that both have any of the white spotting alleles (W/n), will result in a failed pregnancy on the 4th day if the foal is W/W (25% chance). A homozygous white spotting foal will, therefore, never be born.
Below, the resulting phenotype of each genotype is listed:
- W21/Wx = Failed pregnancy
- W21/n = White spotting 21
- n/n = No white spotting
W21 can be tested at the Laboratory.
W21 can of course also be present together with other KIT alleles - however, since they are located on the same gene, horses can only be heterozygous:
- TO/W21 = Tobiano white spotting 21
- RN/W21 = Roan white spotting 21
¶ Breeds
The founder of W21 is the Icelandic Horse Ellert frá Baldurshaga. The following table lists all breeds that can currently have the W21-allele in-game.
| Breeds |
| Akhal-Teke Horse |
| Arabian Horse |
| Brabant Horse |
| Brumby Horse |
| Camargue Horse |
| Cleveland Bay |
| Exmoor Horse |
| Finnhorse |
| Fjord Horse |
| Friesian Horse |
| Haflinger Horse |
| Icelandic Horse |
| Irish Cob Horse |
| Kladruber Horse |
| Knabstrupper |
| Lipizzaner |
| Lusitano |
| Mongolian Horse |
| Mustang Horse |
| Namib Desert Horse |
| Noriker Horse |
| Norman Cob |
| Oldenburg Horse |
| Pantaneiro Horse |
| Pura Raza Española |
| Quarter Horse |
| Shetland Pony |
| Shire Horse |
| Suffolk Punch |
| Thoroughbred |
| Trakehner Horse |
| Welsh Pony |
¶
References
- Bellone R., Sponenberg D. P., Equine Color Genetics, 4th Edition, 2017, Wiley-Blackwell
- Haase B. et al., A novel KIT variant in an Icelandic horse with white-spotted coat colour, Animal Genetics, 2015
- The University of Sydney, Online Mendelian Inheritance in Animals (OMIA); https://omia.org/OMIA000209/9796/; Access: December 2022