Four polymorphic markers on rat chromosome 12 form a single linkage group

Correlation between genetic and cytogenetic maps of the rat

To correlate rat genetic linkage maps with cytogenetic maps, we localized 25 new cosmid-derived simple sequence length polymorphism (SSLP) markers and 14 existing genetic markers on cytogenetic bands of chromosomes, using fluorescence in situ hybridization (FISH). Next, a total of 58 anchor loci, consisting of the 39 new and 19 previously reported ones, were integrated into the genetic linkage maps. Since most of the new anchor loci were developed to be localized near the terminals of the genetic or cytogenetic maps for each chromosome, the orientation and coverage of the whole genetic linkage maps were determined or confirmed with respect to the cytogenetic maps. Thus, we provide here a new base for rat genetic maps.

Phylogenetics of the laboratory rat Rattus norvegicus

A genealogic tree was constructed for inbred strains of the laboratory rat, including 63 strains and 214 of their substrains. Information on genetic and biochemical marker typings of these lines was collected from the literature and from the World Wide Web. Data on 995 polymorphisms were processed into a phylogenetic distance matrix, and a tree was obtained by the Fitch-Margoliash distance matrix method. The inbred strains of the laboratory rat showed an average polymorphism for pairwise comparison of 53%. Strain BN showed the highest genetic divergence from all the other ones. Comparison with the mouse phylogenetic tree indicated that laboratory rats possess a higher diversity than inbred strains of mice not derived from wild species. These results provide a phylogenetic basis in the choice of rat strains for genetic linkage experiments.