Dominant White 21 (W21)
Dominant White 21, also known as W21, is a dominant white spotting pattern that can appear on all three base coat colors.
W21 horses typically have irregular white markings with jagged or roaned edges, often including extensive facial markings, white legs, and scattered white hairs throughout their body. The pattern can sometimes be confused with Sabino (SB1), Roan (RN), or Dominant White 8 (W8) due to its similar appearance.
How W21 Works In-Game
In game, W21 horses can display extensive white ticking and irregular patches throughout their coat, giving them a roaned appearance. This gene is not to be confused with the actual Roan (RN) gene however, as the two are genetically different.
The amount and distribution of white can vary, with some horses displaying only scattered white hairs and others having much more extensive white markings across their body.
W21 does not change the horse's underlying base coat color, although other white spotting patterns and modifiers may influence the resulting appearance, especially if multiple white markings are stacked.
W21 Inheritance
Because W21 is dominant, only one copy is needed for the pattern to visually show on a horse.
- W21/W21 - The horse has two copies of W21. This combination is treated as a homozygous lethal in game.
- W21/n - The horse has one copy of W21 and will have a 50% chance of passing W21 to its offspring.
- n/n - The horse does not have the W21 gene and will not visually display it or be able to pass it to its offspring.
Embryonic Lethals
W21 is believed to be potentially embryonic lethal when a horse inherits two copies of the gene. This means that an affected embryo may fail to develop, resulting in loss of the pregnancy before the foal is born.
Because W21 and other Dominant White variants, such as W8, affect the same KIT gene, inheriting two different variants may also carry a risk of embryonic lethality. However, combinations such as W8/W21 have not been confirmed to be lethal in real horses, and not all Dominant White combinations have the same effects.
In game, horses carrying W21/W21, W8/W8, or a combination (W8/W21) will result in a lethal combination. This would typically result in the foal passing away before it is born, however in game the foal will display similarly to one impacted by LWO (Lethal White Overo Syndrome). It will be born, however will pass away before growing into an adult.
When breeding a horse carrying W21 (W21/n) with a horse carrying W8 (W8/n), the resulting probabilities are:
- 25% - W8/W21 - One copy of each variant. Lethal combination in game.
- 25% - W21/n - One copy of W21, allowing the horse to display the pattern.
- 25% - W8/n - One copy of W8, allowing the horse to display the pattern.
- 25% - n/n - No copies of either variant.
Breeding two horses carrying the same variant (W21/n × W21/n or W8/n × W8/n) also produces a 25% chance of inheriting two copies of that variant.
Because of this, breeding two horses carrying W8 or W21 together comes with a risk of producing a foal inheriting a lethal combination. You may still breed these horses together, however you understand the risks associated with doing so.
Genetic Testing
W21 is a genetically identified white spotting pattern associated with the KIT gene in real horses. The gene was originally identified in Icelandic Horses.
In our genetics system, W21 is a testable white marking. Players can have their horses genetically tested at a veterinary office to determine whether they carry the W21 gene.