It’s a curious fact of biology: In yeast, only one in five genes is essential. If any of the approximately 1,200 critical genes are destroyed (out of 6,000), the result is death. Remove one of the others, and the yeast soldiers on.

The same is not always true, however, if a pair of nonessential genes is removed — sometimes, death comes quickly. In these cases, it’s likely that the genes have similar roles. They might both take out the cell’s garbage, for instance, or fix damaged DNA. The loss of one might not be deadly — the other could pick up the slack. But the loss of both is catastrophic.

Can we use what happens when a pair of genes is destroyed to find out their function? This is the question that Charles Boone and Brenda Andrews, biologists at the University of Toronto, began to ask themselves about 17 years ago. If you know what one gene is doing in the cell, and destroying it kills the cell only if another, more mysterious gene goes too — can that give you clues to what the mystery gene does?

To answer the question, they began to orchestrate a precise campaign to destroy, two by two, all the genes in yeast. Using a fleet of yeast-growing robots, they created approximately 23 million strains of yeast, each effectively missing a pair of genes. By watching to see whether the yeast lived, died or grew sickly, the researchers generated data about the existence of relationships between the genes.

Now Boone, Andrews and a large team of collaborators have published in Science a sprawling report on the nearly two-decade-long set of experiments. In all, they found 550,000 pairs that, when removed, result in sickness or death. This network of genetic connections reveals a previously hidden scaffolding that underlies the operation of the cell. “The complete picture,” Boone said, “clearly shows a beautiful hierarchical structure.”

Over here are the genes involved in taking out the cell’s garbage, and over there are the genes responsible for its metabolism. Zoom out from one cluster of genes, and you’ll find the ones involved in the larger process the cluster is nested in. Zoom out from those and you’ll find all the ones that function alongside them in the same compartment of the cell. There’s something vertiginous in this view of life, a feeling that all the layers of complexity that let the organism thrive are there to look through, just as they were laid down by evolution.

As beautiful as the bird’s-eye view of the cell is, this work goes beyond biological voyeurism. This information can tell us about the evolution of the cell and, potentially, about how things go wrong in disease.