Figure 3: Snowflake versus aggregate life cycles.

Segregation of de novo mutations into mutant-only clusters is inevitable in snowflake yeast, but unlikely in aggregates. Shown are the chimeric clusters containing wild-type (tan) and mutant (green) lineages. Snowflake clusters reproduce by severing a single cell–cell connection (cells with a dashed outline marked 0′), resulting in a unicellular genetic bottleneck. Only two types of propagule can be generated: those with an ancestral cell at the bottleneck (resulting in a purely ancestral propagule) or those with a mutant cell at the bottleneck (resulting in a purely mutant propagule). In contrast, the aggregative life cycle has no bottleneck. Instead, propagules are formed by randomly selecting cells from within the cluster.