Lethal dominant white in horses.

The research article discusses the genetic factors involved in the appearance of the “dominant white” color in horses, distinguishing it from other types of white such as albino or progressive silvering. This dominant white color is associated with blue or colored eyes and pink skin and is evident at birth.

Background Information

• The document opens by explaining that although an American Albino Horse Club exists, there’s no identified albino mutation in horses. It observes that “albinos” or “blancos” and “cremellos” are actually colored horses that carry two copies (homozygous) of a partially dominant dilution gene, D. This gene dilutes their color to almost white or pale cream, accompanying pinkish skin and blue eyes.
• The researchers then refer to earlier studies showing that in horses carrying a single copy of the gene (heterozygous), this gene turns a horse that would have been chestnut into a yellowish color known as Palomino in the U.S.
• They also mention another type of white coloration in horses, termed “progressive silvering”, which is observed in horses that progressively gain white hairs as they age. However, the focus of the paper is on the genetically different dominant white color, which is apparent at birth and is associated with blue, brown, hazel or other colored eyes and pink skin.

Earlier Studies

• The study points out that Sturtevant was the first researcher to identify the dominant white color in horses and ascribed it to a gene, he called ‘W’.
• The paper also references Wriedt’s investigation on Frederiksberg’s white horses. Wriedt had deemed these horses recessive whites, with various phenotypes including pure white, white with gray spots or gray-white. Heterozygotes were thought to differ from diluted gray to full color.
• However, with more recent evidence, the paper challenges this belief, stating that Wriedt’s conclusions seem to be incorrect. Nonetheless, the German researcher earns recognition for another revelation – that a lethal gene in the Frederiksberg stud was causing poor breeding performance.