A RADIATION HYBRID MAP OF HUMAN CHROMOSOME-18

A human x Chinese hamster (CH) somatic cell hybrid subclone deficient in HPRT and containing only human chromosome 18 was irradiated with 70 00 rad and fused to a thymidine kinase deficient CH cell line. Radiati on-rescued hybrid cell lines, selected in HAT medium, were analyzed fo r human DNA with human interspersed-repeat sequence primers. Size and number of human chromosome fragments retained in a subset of hybrids w ere determined by FISH. A panel of 98 radiation hybrids (RH) was selec ted and analyzed for 90 chromosome 18-specific STSs by PCR, and for th e D18Z1 centromeric marker by Southern blotting. STSs were developed f rom previously mapped RFLP loci and from published sequences. In addit ion, 32 novel STSs were generated from an 18-specific lambda library a nd from 18-specific YACs previously localized to chromosome bands by F ISH, Marker retention frequency varied from 8-65 % with an average of 24 %. In selected RH the STS typing data were correlated with the chro mosome 18 regions retained using 'reverse FISH' of IRS-PCR products fr om the RH to normal metaphase chromosomes. The order and intermarker d istances of loci were determined using two-point and multipoint maximu m likelihood methods. The resulting RH map covers most of chromosome 1 8 with four groups of tightly linked markers and three regions of loos ely linked markers, one around the centromere and two on the long arm. More than a third of the markers are polymorphic and allow integratio n with the linkage map. This RH map provides a framework for establish ing a clone contig of the entire chromosome 18.