Advances in livestock nuclear transfer

Cloning and transgenic animal production have been greatly enhanced by the development of nuclear transfer technology, In the past, genetic modificati on in domestic animals was not tightly controlled, With the nuclear transfe r technology one can now create some domestic animals with specific genetic modifications, An ever-expanding variety of call types have been successfu lly used as donors to create the clones. Both cell fusion and microinjectio n are successfully being used to create these animals, However, it is still not clear which stage(s) of the cell cycle for donor end recipient cells y ield the greatest degree of development, While for the most part gene expre ssion is reprogrammed in nuclear transfer embryos, all structural changes m ay not be corrected as evidenced by the length of the telomeres in sheep re sulting from nuclear transfer. Even after these animals are created the que stion of "are they really clones?" arises due to mitochondrial inheritance from the donor cell versus the recipient oocyte, This review discusses thes e issues as they relate to livestock.