Different S. rosetta cell types disproportionately upregulate genes with different evolutionary histories. (a) The majority (57%) of S. rosetta genes are ancient and evolved prior to the divergence of choanoflagellates, metazoans and fungi. An additional 5% of S. rosetta genes emerged along the stem lineage leading to S. rosetta and metazoans and 6% evolved along the choanoflagellate stem lineage. Thirty-one percent of genes in the S. rosetta genome are apparently unique to S. rosetta. (b-e) The evolutionary history of S. rosetta genes upregulated in different cell types (pie charts) and the percent enrichment (y-axis) relative to the S. rosetta genome (bar graphs). Color code: red, S. rosetta-specific genes; blue, genes restricted to choanoflagellates; yellow, genes uniquely shared by choanoflagellates and metazoans; green, genes restricted to opisthokonts. (b) Thecate cells. (c) Colonies and swimming cells. (d) Colonies (rosettes and chains). (e) Swimming cells. **P < 0.01.