A genetic mutation in single-celled yeast turns it into a multicellular organism — hinting at how multicellularity might have evolved.
William Ratcliff at the Georgia Institute of Technology in Atlanta and his co-workers studied a strain of yeast (Saccharomyces cerevisiae) in which the daughter cells remain attached to the mother cells after dividing, resulting in multicellular 'snowflake' yeast. By mathematically modelling the way that clusters break off, the authors conclude that this way of growing makes the cells in each cluster genetically similar. This allows natural selection to act on the clusters rather than on individual cells, speeding up multicellular evolution. A mutation in a gene encoding the protein ACE2 causes the clusters to form.
After 60 days of selection (400 generations), the yeast evolved bigger cells (pictured, right; scale bars are 50 μm) compared with those at 14 days (left). The results show how a single mutation can create multicellular clusters and set the stage for the future evolution of organismal complexity.