Figure 3: Comparison of developmental trajectories between species.

After inferring developmental trajectories for the cell types of interest in two different species, one can compare these trajectories to identify the developmental mechanisms that led to the evolution of the new cell type. Based on the developmental trajectory, one can distinguish between cases of lineage duplication and extension, as well as instances where cells that undergo apoptosis in one species survive in the other, and define key splits in the trajectory of evolutionary related cells. Studying the differential expression of genes along the trajectory, one can identify putative transcription factors that differ between species and may have been involved in the key splits.