Since the mid 1980s, technology has been developed to transfer the nucleus from either a blastomere (cells from early, and presumably undifferentiated cleavage stage embryos) or a somatic cell (fibroblast, skin, heart, nerve, or other body cell) to an enucleated oocyte (unfertilized female egg cell with the nucleus removed). This “nuclear transfer” produces multiple copies of animals that are themselves nearly identical copies of other animals (transgenic animals, genetically superior animals, or animals that produce high quantities of milk or have some other desirable trait, etc.). This process is also referred to as cloning. To date, somatic cell nuclear transfer has been used to clone cattle, sheep, pigs, goats, horses, mules, cats, rabbits, rats, and mice.