The Manx taillessness gene is dominant and highly penetrant; kittens from two Manx parents are generally born without any tail. Being homozygous for (having two copies of) the gene is usually lethal "in utero", resulting in miscarriage. Thus, tailless cats can carry only one copy of the gene. Because of the danger of having two copies of the taillessness gene, breeders avoid breeding two entirely tailless Manx cats together. Because neither parent carries the tailless allele, a fully tailed Manx bred to another fully tailed Manx results in all fully tailed kittens.