T gene belongs to a T-box gene family encoding transcription factors important during the embryonic development. T gene mutation was first found in Pembroke Welsh Corgis and afterwards in many other breeds. The mutation is dominantly inherited and results in a short-tail or tailless phenotype. Homozygosity for the mutation causes emryonic or postnatal lethality. Confirmation of the natural origin of a short tail is a necessity for breeders, because an increased number of countries is prohibiting cutting tails.
Hytönen, M.K., Grall, A., Hédan, B., Dréano, S., Seguin, S.J., Delattre, D., Thomas, A., Galibert, F., Paulin, L., Lohi, H., et al. (2009). Ancestral T-box mutation is present in many, but not all, short-tailed dog breeds. J. Hered. 100, 236–240.
Joanna Gruszczyńska, A.C. (2011). A molecular test for the detection of the C295G mutation in the T gene responsible for shortened tail and taillessness in the Pembroke Welsh Corgi. Annals of Warsaw University of Life Sciences – SGGW Land Reclamation 49, 35–43.