Chromosomal position of the 'donor gene' and the relative age of the gain event. The graph shows the fraction of events for which the 'donor gene' of the gained domain is identified, and is on the same chromosome as the gene with the gained domain, with respect to the relative age of the gain event. The gain events were divided into five groups according to the expected age of the event as judged by the TreeFam phylogeny. The x-axis shows the evolutionary group in the human lineage to which descendants of the gain event belong, and the y-axis shows the percentage of gain events in each evolutionary group for which both of the conditions were valid: we were able to find the donor gene and the donor gene was on the same chromosome as the gene with the gained domain. This was true for 3 out of 9 gain events in primates, 2 out of 20 in mammals, 7 out of 121 in vertebrates, 1 out of 27 in Bilateria and 1 out of 55 in all animals. Estimated divergence times (in millions of years ago (mya), as taken from Ponting ) are: 25 mya for primates, 166 mya for mammals, 416 mya for vertebrates and 700 mya for all animals (we were not able to estimate the divergence time for Coelomata).