Four restriction fragment length polymorphisms revealed by probes from a single cosmid map to human chromosome 12q.

Human gene mapping would be greatly facilitated if marker loci with sufficient polymorphism information content were generally available. As a source of such markers, we have used cosmids from a human genomic library. We have used a rapid method for screening random cosmids to identify those homologous to genomic regions especially rich in restriction fragment length polymorphisms (Litt and White 1985). This method allows whole cosmids to be used as probes against Southern transfers of genomic DNA; regions of cosmid probes homologous to repeated genomic sequences are rendered unable to anneal with Southern transfers by prehybridization of the probes with a vast excess of non-radioactive genomic DNA. From one cosmid (C1-11) identified by this procedure, we have isolated four single-copy probes, each of which identifies a polymorphic locus. Despite the existence of some linkage disequilibrium in this system, the polymorphism information content was computed as 0.73. Using a somatic cell hybrid mapping panel, we have mapped probes from cosmid 1-11 to human chromosome 12q. Additionally, in situ hybridization of the whole cosmid to metaphase spreads allowed more precise assignment of the locus to the region 12cen----q13. The locus revealed by probes from cosmid 1-11 has been designated D12S6.