mutation pathway

Blount ZD, Borland CZ & Lenski RE 2008 Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli. PNAS 105:7899-7906.

• the phenotypic change required two mutations, one of which occurred during the culture growth before plating and the other after plating
• results instead support the hypothesis of historical contingency, in which a genetic background arose that had an increased potential to evolve the Cit⁺ phenotype