The reason Manx cats don't have tails is primarily due to a genetic mutation. This mutation occurs in the genes that form the spine; the gene marked "M" causes abnormal development of the coccyx and sacral vertebrae (the spinal region in front of the tail).
All Manx cats have one mutated gene and one normal gene. The mutated gene is dominant, which means that the tailless trait is easily passed on to the next generation.
