Résumé
Two populations which have diverged from an ancestral population may come back into contact due to humanaction via stocking or introduction programs. We report here a method to measure genetic admixture in such situations based on juxtaposed microsatellite systems (JMSs). A JMS is composed of two microsatellite repeatarrays separated by a sequence of less than 200 bp. The advantage of a JMS stems from the superior genealogical information carried by the two microsatellite sites to that carried by just one. If five assumptions are fulfilled, JMSs provide reliable diagnostic markers which eliminate the need to know the genetic structure of the native population in the absence of admixture. Simulations show that optimal features at both microsatellite sites of the JMS are theoccurrence of multistep mutations, moderately high mutation rates, and limited allele size constraints. Optimal demographic features include a relatively large number of generations since the separation of the alien and native populations and small population sizes, especially for the alien population. Substantial sampling of the alien population is also necessary