Yeast artificial chromosomes (YACs) were made from a total EagI digest of DNA from a mouse-human chromosome 21 hybrid cell line. Approximately 3750 YACs, corresponding to 75-125 human YACs, with an average size of approximately 100 kb were recovered. Southern hybridization indicates that the chimera frequency in this library may be less than 3%. Thirty-four of the human Eag I YACs were regionally assigned by a number of methods. Some YACs were regionally assigned to one of six chromosome regions by hybridization of Alu -PCR products from the YAC against Alu-PCR-amplified DNA from a panel of hybrid cell lines that contain various parts of chromosome 21. Additional YACs were regionally assigned by fluorescence in situ hybridization using either biotinylated Alu-PCR products or yeast genomic DNA from the YAC-containing strains as probes. The regionally assigned Eag I YACs are located preferentially in two regions of the chromosome: near the q telomere and in the p-arm ribosomal gene region.
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