Developmental hourglass: Verification by numerical evolution and elucidation by dynamical-systems theory
Fig 5
The variance of gene expression patterns over 1000 clones, i.e., those generated from the same genotype but with different initial conditions.
The horizontal axis represents developmental time, and the vertical axis represents the total variance in gene expression over all cells, i.e., the summation of variance over cells, over genes, and over clones (see also Methods). As specific examples, the data of three different individuals are indicated by different colors. The blue stripe indicates the typical range of observed developmental bottlenecks (average ± standard deviation), as obtained by comparing individuals belonging to blue triangle A in the phylogenetic tree in Fig 3, which exhibits clear hourglass-like developmental correlations. Here, the initial conditions are chosen by adding Gaussian distribution noise with a variance σ = 0.1. (The details of the computation scheme are presented in the Methods section).