ABSTRACT
In the past, it was considered impossible to produce cloned animals derived from differentiated somatic cells. However, since the birth of a cloned sheep [1], successful cloned animals have been reported in mice [2], cattle [3], goats [4], pigs [5,6], cats [7], rabbits [8], mules [9], horses [10], rats [11], and deer (press released). Before cloned animals derived from somatic cells, blastomeres from undifferentiated early stage embryos were mainly used as the nuclear donors. With the animal species mentioned here, embryo clones had been produced from embryos of different early stages.
