MICROSATELLITE DNA IN FISHES

For the last 30 years, attempts have been made to discriminate among f ish populations by using molecular markers. Although some techniques h ave proved successful in certain circumstances, the consistent trend t o newer markers among fishery geneticists highlights the general lack of resolving power observed with older technologies. The last decade h as seen the increasing use of satellite DNA in investigations of genet ic variability and divergence. Applications to fish and fisheries-rela ted issues initially concentrated on minisatellite single-locus probes . Although minisatellites have successfully addressed a number of fish ery-related questions, this class of satellite DNA has not been widely adopted by fishery geneticists. Most of the current research effort i s concentrated on another class of satellite DNA called microsatellite s. The large interest in microsatellite loci is largely due to the ver y high levers of variability that have been observed and the ability t o investigate this variation using PCR technology. The isolation and a pplication of microsatellites to research fields as diverse as populat ion genetics, parentage analyses and genome mapping are reviewed. Desp ite the undisputed advantages that the marker possesses, there are a n umber of potential problems associated with investigating variation at microsatellite loci. Statistical considerations (e.g, appropriate sam ple sizes, number of loci and the mutation model assumptions on which the estimate is based) have not been considered in detail yet and the problems are often exacerbated in fish species, as some species show v ery large numbers of alleles at microsatellite loci. These issues and others, e.g. null alleles, are reviewed and possible solutions are pro posed.