Bob tail (short tail, brachyury)

 

Gene: TBXT

Transmission: Autosomal dominant

For an autosomal dominant genetic disease, an animal must have at least one copy of the mutation in question to be at risk of developing the disease.  Animals with two copies of the mutation generally have more severe symptoms and an earlier onset of the disease than animals with just one copy of the mutation.  One or both of the parents of an animal with the mutation has one or two copies of the mutation.  Animals that have one or two copies of the mutation can pass the mutation on to future generations.

Mutation: Substitution, TBXT gene; c.295 C>G, p.(Ile63Met), exon1, chr.1

Medical system: Skeletal

Breeds:

Age of onset of symptoms: From birth

The TBXT gene, formally known as the T gene encodes a protein called the T-box transcription factor T, also known as the Brachyury protein.  The Brachyrury protein is involved in the development of the mesoderm and responsible for the number of vertebrae in the posterior part of the body.  A natural mutation in the canine TBXT gene results in a short tail phenotype that has been selected for in a number of breeds.  If the animal is heterozygous for the mutation it will have a shorter tail than normal, although the exact length can be variable, from shortened (brachyury) to absent (anury).  When there are two copies of the mutated gene, this situation is lethal to the embryo.  Therefore, breeding two dogs with a short tail (Bobtail) will decrease the size of litters.

Mutations in the TBXT gene are also responsible for the short tail phenotype seen in several cat breeds such as the Manx cat.

 

References:

OMIA link: [0975-9615]

Dreger DL, Hooser BN, Hughes AM, et al. (2019) True Colors: Commercially-acquired morphological genotypes reveal hidden allele variation among dog breeds, informing both trait ancestry and breed potential. PLoS One 14:e0223995.  [pubmed/31658272]

Hytonen MK, Grall A, Hédan B, et al. (2009) Ancestral T-Box mutation is present in many, but not all, short-tailed dog breeds.  Journal of Heredity 100(2):236-240. [pubmed/18854372]

Haworth K, Putt W, Cattanach B, et al. (2001) Canine homolog of the T-box transcription factor T; failure of the protein to bind to its DNA target leads to a short-tail phenotype.  Mammalian Genome 12:212-218. [pubmed/11252170]