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How Low Can It Go?

How many genes are needed to sustain an organism? As Carl Zimmer notes in the New York Times that number may be surprisingly small and, ultimately, irrelevant.

Tremblaya princeps only has 120 protein-coding genes, but that the organism is quite specialized, Zimmer notes. It lives only on the mealybug, in a co-dependent fashion. But, he adds, a third player — a bacterium called Moranella endobia, coming in with 406 genes — is actually needed for T. princeps to transform sap into food for the mealybug. As these organisms became entwined, they lost genes they once had.

"[T]he concept of a minimal genome, while provocative, is ultimately a dead end," Zimmer says. "Life does not exist in a laboratory vacuum, where scientists can pare away genes to some Platonic purity. Life exists in a tapestry, and the species with the smallest genomes in the world survive only because they are nestled in life's net."