Scientists around the world are anticipating the results of a Chinese study that would mark the first time DNA in a human embryo has been modified in a way that would carry into future generations. Although the embryos would be for study only, and not intended for implantation, the research would mark a significant milestone: the first time human DNA had been altered so substantially that it would change the “germ line” — the eggs or sperm of any child produced from the embryo.