The T Locus (Natural bobtail) trait test reliably determines if a dog has one of the following genotypes at the T locus:
This dog carries two copies of the dominant T Allele which is lethal causing pups to die In Utero.
Interpretation: Embryonic lethal
This dog carries one copy of the dominant T allele and one copy of the recessive t allele which produces a natural bobtail. This dog will pass on the T allele to 50% of its offspring and the t allele to 50% of its offspring.
This dog carries two copies of the recessive t allele which results in a tail of normal length (no bobtail). This dog will pass on the t allele to 100% of its offspring.
Interpretation: Normal tail
The T Locus (Natural bobtail) impacts the length of the tail in many breeds of dog. A DNA variant in the T gene, an important gene during early embryogenesis, disrupts the development of the dog’s tail and can result in a congenitally short (bobtail) or completely absent tail. The natural bobtail variant is inherited in an Autosomal Dominant fashion meaning only one copy of the T gene variant is required to produce a natural bobtail. However, inheriting two copies of T is not compatible with life causing pups to die In Utero. Therefore, breeding two dogs with natural bobtails (T/t) may result in reduced litter sizes.
Genetic testing of the T gene will reliably determine whether or not a dog is a genetic Carrier of the variant that produces a natural bobtail or if the tail has been docked. Breeding two dogs with natural bobtails will result in slightly reduced liter-sizes because about 25% of the puppies will inherit two copies of the T Allele and will die In Utero. However, about two-thirds of the surviving litter will be Heterozygous T/t have natural bobtails and one-third of the liter will be Homozygous t/t and have normal length tails.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Hytonen MK, Grall A, Hedan B, Dreano S, Seguin SJ, Delattre D, Thomas A, Galibert F, Paulin L, Lohi H, Sainio K, Andre C. Ancestral T-box mutation is present in many, but not all, short-tailed dog breeds. J Hered. 2009 Mar-Apr; 100(2):236-40.