My most recent Technology Feature, on the technology of genome synthesis, describes advances in the field of large-scale genome hacking. Researchers are rewriting the genomes of organisms from E. coli to yeast, with millions of bases written from scratch. Now, through projects like Genome Project-write, they are turning their attention to even more complex organisms, with concomitantly larger genomes.

How, though, does one actually write a genome? As I note in the article, researchers don’t do that in one step. The molecules are assembled hierarchically, from synthetic oligonucleotides to ever larger pieces, first in a test tube and ultimately in living cells.

That said, it is possible to purchase “gene-sized” pieces of synthetic DNA. But, since DNA today is synthesized mostly using the same error-prone phosphoramidite chemistry researchers have used for decades, the question is: how are those molecules made?

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