Taillessness in a cloned cow is not genetically transmitted

Somatic cell nuclear transfer (SCNT), commonly referred to as cloning, results in the generation of offspring that, except for mitochondrial DNA, are genetically identical to the nuclear donor. We previously used a genetically modified bovine cell line as the donor for SCNT and obtained a calf, named Daisy, which was born without a tail. To determine whether the missing tail is a result of the genetic modification, we performed recloning experiments using as donors for SCNT either cells from a sacrificed pregnancy from a second clone (Daisy’s ‘twin’ clone) or cells from the tailless calf. Cloned fetuses from aborted pregnancies and a cloned live calf that died shortly after birth were examined and shown to all possess tails. Hence, the observed phenotype of Daisy’s lacking tail is not due to the introduced transgene or a mutation present in the cell that was used for her production. Rather, the missing tail must have arisen from an epigenetic reprogramming error during development.