Swollen down plumules, an embryonic lethal condition characterized by an enlargement of the dermal pulp cavity of down feathers, has been observed in a subline of turkeys. The lethality of the condition is expressed between 20 days of incubation and the time of pipping. Phenotypic variation of the disorder is expressed in the number of pterylae that contain the abnormal down plumules. The disorder is inherited as an autosomal recessive trait, and the gene symbol, sdp, is proposed.