The equilibrium distribution for a generalized Sankoff-Ferretti model accurately predicts chromosome size distributions in a wide variety of species

Sankoff and Ferretti (1996) introduced several models of the evolution of c hromosome size by reciprocal translocations, where for simplicity they igno red the existence of centromeres. However, when they compared the models to data on six organisms they found that their short chromosomes were too sho rt, and their long chromosomes were too long. Here, we consider a generaliz ation of their proportional model with explicit chromosome centromeres and introduce fitness functions based on recombination probabilities and on the length of the longest chromosome arm. We find a simple formula for the sta tionary distribution for our model which fits the data on chromosome length s in many, but not all, species.