The Peruvian Inca Orchid Dog, Xoloitzcuintle, American Hairless Terrier and Chinese Crested Hairless are the four hairless breeds of dog that we know of. Three of them have dominant hairlessness, which means that they need only one copy of the gene to be hairless.

The one breed left out of this scenario is the American Hairless Terrier (the rest are heterozygous for hairlessness). If one of them was homozygous with two copies of the hairless gene, they’d be re-absorbed into the womb as embryos because of what’s called the “embryonic lethal gene.” The American Hairless Terrier is the truly unusual breed here because it’s the only known example of recessive hairlessness in dogs, and that means a dog has to have two copies of the gene in order to express it as a phenotype (the gene you see). It’s not a lethal gene, unlike dominant hairlessness, and because all hairless American Hairless Terriers are homozygous, coated puppies will never appear when a hairless dog is bred to another hairless dog.

Got that?

Image of a Sugar Skull American Hairless Terrier Brooch by Emily Rose.