In a comparative map, the number of translocations in the evolutionary history of a chromosome can be estimated solely on the basis of the conserved syntenies it contains. This estimate, subtracted from the number of conserved segments, then allows the estimation of the number of inversions that have affected the chromosome. Summing these estimates over all chromosomes provides a startlingly accurate estimator (as assessed by simulation) of the total number of rearrangements of each type occurring in the evolutionary divergence of two genomes.