In a package of seven papers published Thursday in the U.S. journal Science, researchers from the Synthetic Yeast Genome Project announced that they have successfully synthesized five new yeast chromosomes, meaning that 30 percent of a key organism’s genetic material has now been swapped out for engineered replacements. By the end of this year, this international consortium, led by geneticist Jef Boeke of the New York University, hoped to have designed and built synthetic versions of all 16 chromosomes, the structures that contain DNA, for the one-celled microorganism, Baker’s yeast.