The many problems of somatic cell nuclear transfer in reproductive cloning of mammals.

In 1996, when Dolly the sheep was born, a new, utopian era was expected to begin. Science fiction and popular culture instantly threatened the public with shortly upcoming human clones, portraying it as a very easy and instant procedure. Practice has proven otherwise; it exposed how little is known about the early development of mammals and epigenetic reprogramming. Unfortunately, somatic cell nuclear transfer success rate in mammals has not changed much since its very beginning. It is not uncommon that hundreds of oocytes need to be reconstructed to obtain a single live birth. In this review we provide a brief summary of the progress and problems of the field; beginning with selection of the donor cells and their susceptibility to different methods of epigenetic reprogramming; methods of the later gene activation, placental abnormalities, and their possible causes; to health issues that such offspring is prone to.