Categories: Skeleton phene (incl. short stature & teeth) , Limbs / fins / digit / tail phene

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal dominant

Disease-related: yes

Key variant known: yes

Year key variant first reported: 2023

Species-specific name: Also known as Rumplessness

Species-specific description: See also OMIA:002845-9031 : Tail feathers, absent in Gallus gallus (chicken) which is also called rumpless but with Z-linked mode of inheritance and related to abnormal tail feather development without skeletal changes.

History: Davenport (1906), pp. 61-62, provided an extensive history of this trait: "Rumplessness may be found in any race. It has cropped out in two of the 800 fowl bred at this station in the past year-hybrids derived from the Minorca-Polish and the Leghorn-Houdan crosses. It seems like a misuse of the term breed to speak of a "Rumpless breed," as poultry books do. The characteristic is referred to by Aldrovandus in 1645, by Temminck, and by other early writers. Its origin has been ascribed to Persia, to Ceylon, and to China; doubtless it occurs in all these places as well as in many others. Taillessness early appeared among fowls in America. Clayton (1693, p. 992) asserted that he had observed that in" Virginia" most of the cocks and hens were without tails, and Wright states that he was informed by a West Indian in 1872 "that the greater number of fowls in his own neighborhood had no tails." Darwin (1876, Chapter VII) refers to this characteristic and states that one bird he examined had no oil gland; the same is true of the three rumpless Games that I have had. Among the poultry books that describe the "breed" quite fully are Tegetmeier (1867, pp. 230-232), Baldamus (1896, pp. 170-172, "Kaul oder Kliitthiihner"), Diirigen (1886, pp. 98-100), Wright (1902, p. 481), and Weir-Johnson-Brown (1905, pp. 1016-1017)."

Inheritance: Davenport (1906) provided evidence that "Rumplessness in a Game fowl was recessive to the tailed condition of Leghorn, Cochin, Frizzle, and Nankin". However, he also recorded that "Regarding the inheritance of this characteristic, statements are not in accord. Tegetmeier (p. 231) says: "A friend of mine purchased a successful pen [of Rumpless fowl] at a poultry show, taking them away to a walk where no other fowls ever trespassed, and yet the chickens were, in a considerable number of instances, furnished with fully developed tail feathers, being not rumpless. On inquiry of the previous owner, he stated: "Mine have always done so from the first time I kept them; but the tailed birds will very probably produce rumpless chickens." Three such birds were purposely retained, and they produced the next year more than twenty youngsters, all of which but one were rumpless and destitute of tail feathers."" Davenport continues: "The foregoing experiment would seem to prove that the rumpless parents were heterogametous, and that while rumplessness is dominant the recessive condition of tail is here prepotent (Castle, 1905). Darwin (1876, Chapter VII) possessed a rumpless bird which "came from a family where, as I was told, the breed had kept true for twenty years; but" he adds, "rumpless fowls often produce chickens with tails." The breeding true of a character may mean either that it is dominant and homogametous in this respect or that it is recessive. Durigen (1886, p. 99) states that a rumpless cock mated with a tailed hen produces not exclusively rumpless, but a fair percentage of them, and Wright (1902, p. 481) says that" a Rumpless fowl crossed with any other generally produces a large majority of Rumpless birds." All of the foregoing results are consonant with the conclusion that rumplessness is typically dominant, but that the recessive full tail may be prepotent." Rumpless was included by Bateson (1909) in a long list of chicken traits showing autosomal dominance Mendelian inheritance; in this case autosomal dominance. Dunn (1925) reported autosomal dominance in mixed-breed chickens, and occasional cases in which the trait is not inherited. Warren (1933) provided substantial evidence of autosomal dominant inheritance from backcrossing heterozygotes to homozygous recessives, but did not mention the breeds involved. Zwilling (1945) reported a recessive form of this trait.

Mapping: Noorai et al. (2012) mapped the dominant form of rumpless in Araucana chickens to chromosome GGA2, and identified a 2.14MB candidate haplotype containing two positional candidate genes, IRX1 and IRX2. More than a decade later, by conducting GWAS and linkage analyses on "a backcross pedigree by intercrossing Piao (rumpless) with Xianju (normal)", Guo et al. (2023) confirmed the mapping of Noorai et al. (2012) and fine-mapped the trait to a 798.5 kb region "(chromosome 2:86.9-87.7 Mb)".

Molecular basis: Within their locational candidate region on GGA2, Guo et al. (2023) identified the likely causal variant as "a 4.2 kb deletion, which was completely associated with the rumpless phenotype. Explorations of the expression data identified a novel causative gene, Rum, that produced a long, intronless transcript across the deletion. The expression of Rum is embryo-specific and that it regulates expression of MSGN1, a key factor in regulating T-box transcription factors required for mesoderm formation and differentiation. These results provide genetic and molecular experimental evidence for a novel mechanism regulating tail development in chicken and report the likely causal mutation for the tail abnormity in the Piao chicken."

Clinical features: Davenport (1906), page 61: "The absence of uropygium is a characteristic that has long been known among fowl, but there seems to be little knowledge of its morphology. In ordinary fowl there are five free caudal vertebrae, followed by a fused portion-the uropygial bone. In the case of a rumpless Game female (No. 119, fig. 45) dissected by me, there are two unsymmetrically formed and intimately fused vertebrae behind the fifteenth synsacral--the posterior limit of the sacral vertebrae. That there are two is shown by distinct transverse processes with spaces of the passage of the nerves. Behind these is a knob of bone about I mm. in diameter. These three elements constitute the entire caudal skeleton. It is profoundly reduced from the normal."

Breeds: Araucana (Chicken) (VBO_0000445), Piao chicken, China (Chicken) (VBO_0006739), Rumpless Game (Chicken) (VBO_0000613).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).

Associated gene: