Biophysics and population size constrains speciation in an evolutionary model of developmental system drift
Fig 1
An overview of the genotype-phenotype map.
The gene regulatory module has as input a morphogen concentration [M](x) that varies approximately exponentially across a 1-dimensional embryo of length L, and outputs a transcription factor [T](x). Spatial gene regulation of T is achieved via a simple Hamming model of protein DNA binding as shown. Fitness is determined by weighting any gene expression in the anterior half of the embryo as positive, and any in the posterior half as negative (as shown bottom left). We show idealised expression profiles that give maximum fitness when gene expression is confined only to the anterior half (bottom middle), and minimum fitness when there is no discrimination between anterior and posterior (bottom right); these translate to log-fitnesses of F = 0 and F = −∞, respectively (see Methods).