Cross-referencing radiation hybrid data to the recombination map: lessons from mouse chromosome 18.

We are building a framework map of known-order anchor markers between the mouse T31 radiation hybrid (RH) panel and the recombination map based on The Jackson Laboratory (TJL) interspecific backcross panels using the established genetic order to evaluate and strengthen the RH results. In making this map comparison, we have elucidated several problems inherent in RH mapping and minimized these by careful attention to data gathering and interpretation methods. We describe lessons and pitfalls of developing radiation hybrid maps, using the example of mouse Chromosome 18, for which we have built a framework map of microsatellite anchor loci spanning the entire chromosome at significant LOD with no gaps. Sixty-five D18Mit- simple sequence length polymorphism (SSLP) markers form a continuous linkage along the T31 RH Chromosome 18 (RH map length 1598 cR, genetic length 41 cM) with all LODs greater than 6. These markers are also placed on TJL interspecific backcrosses, and the order of the markers in the two systems is in complete agreement. We are continuing to cross-reference the RH data to TJL backcross data for the other mouse chromosomes to improve further the power of RH mapping and to integrate more precisely the extensive existing recombination mapping data for the mouse with the incoming radiation hybrid map data.