MICROSATELLITE EVOLUTION - TESTING THE ASCERTAINMENT BIAS HYPOTHESIS

Previous studies suggest the median allele length of microsatellites i s longest in the species from which the markers were derived, suggesti ng that an ascertainment bias was operating. We have examined whether the size distribution of microsatellite alleles between sheep and catt le is source dependent using a set of 472 microsatellites that can be amplified in both species. For those markers that were polymorphic in both species we report a significantly greater number of markers (P<0. 001) with longer median allele sizes in sheep, regardless of microsate llite origin. This finding suggests that any ascertainment bias operat ing during microsatellite selection is only a minor contributor to the variation observed.