The asexual creation of a genetic copy, a capability possessed by plants but not by most animals. Thus, plants generate genetic copies spontaneously, and rooting “cuttings” is widely used by horticulturists to propagate millions of clones annually. In animals, only some lower invertebrates can be cloned by “cutting”; for example, earthworms when bisected will regenerate the missing half, resulting in two whole, genetically identical individuals. However, asexual reproduction and cloning do not normally occur in vertebrates except for the special case of identical twinning. This is despite the fact that individual cells, called blastomeres, within the very early embryo are totipotent; that is, each is capable, if evaluated on its own, of developing into a viable term pregnancy and infant.