The ability to sequence and study whole genomes, coupled with an increased understanding of what genetic information is required for basic biological processes, now provides the possibility of creating—entirely from scratch—novel organisms that have never before existed. Synthetic biology is a new field that seeks to design organisms that might provide useful functions, such as microbes that provide clean energy or break down toxic wastes.

Synthetic biologists have already mixed and matched parts from different organisms to synthesize microbes. In 2002, geneticists recreated the poliovirus by joining together pieces of DNA that were synthesized in the laboratory. Even more impressively, in 2010, Daniel Gibson and his colleagues synthesized from scratch the complete 1.08 million-base-pair genome of the bacterium Mycoplasma mycoides. They started with a thousand pieces of DNA that were synthesized in the laboratory and joined them together in successively larger pieces until they had assembled a complete copy of the genome. Within their synthetic genome, they included a set of DNA sequences that spelled out—in code—an e-mail address, the names of the researchers who participated in the project, and several well-known quotations. Finally, the researchers transplanted the artificial genome into a cell of a different bacterial species, M. capricolum, whose original genome had been removed. The new cell then began expressing the traits specified by the synthetic genome.

Synthetic biology has also been extended to eukaryotic cells. In 2011, geneticists replaced 90,000 bp of the DNA of yeast chromosome 9 and 30,000 bp of yeast chromosome 6 with synthetic DNA. The partially synthetic yeast cells that resulted grew normally and exhibited only minor differences from normal cells in their gene expression. The ultimate goal of these experiments is to replace the entire 12 million-base-pair genome of yeast with human-designed sequences.

412

These types of experiments have raised a number of concerns. The ability to make novel genomes and to mix and match parts from different organisms creates the potential to synthesize dangerous microbes, which might create ecological havoc if they escaped from the laboratory or might be used in biological warfare or bioterrorism. Ongoing discussions among geneticists, ethicists, security experts, and politicians are addressing these concerns and whether synthetic genomes can be safely made and used.