How a person develops from a single fertilized egg to an adult is a fundamental question of biomedical science. Dr. Yang Seok-ju of the Korea Advanced Institute of Science and Technology, Daejeon, South Korea said that it is now possible to precisely identify mutations in a single-cell genome. this technology will allow tracking human embryogenesis in the future with an even higher resolution. The data showed that the frequency of mutations is highest in the first cell divisions, but then decreases to about one mutation per cell later in life. Genome-wide sequencing analysis has shown that our first cells contribute unequally to the development of the embryo and that one cell always leaves more progeny cells than the other after the first division of the embryo. The research could be used to improve understanding of rare diseases caused by abnormalities in embryonic development.