| Emphasis was on breeding for working ability and stamina and, if the stumpy-tailed Halls Heelers were workers of excellence, their taillessness would have been disregarded. |
| Geneticists have determined that taillessness occurred as the result of a spontaneous mutation. |
| There are several different mutations leading to various degrees of taillessness, to bobtails and to curly tails. |
| Manx Syndrome is a normally fatal defect caused by the so-called Manx gene, which causes the taillessness. |
