Map construction has in recent years gained considerable prominence in molecular biology. This is especially true in organisms with large genomes where comprehensive maps are essential for both broad, genome-wide efforts, such as the Human genome Project, as well as focused efforts of gene identification. Current work is severely hindered by the lack of a chromosome-specific large-insert library. One obvious problem is that the Y is always half as abundant as all other autosomes. In collaboration with Drs. Bruce Lahn and David Page, we plan to flow-sort sufficient human Y chromosomes to construct a human Y-specific BAC library. Using about 1 fg of flow -sorted Y chromosomes, the material will be partially digested, size selected at 100kb and greater DNA fragments to ligate into BACvectors. After transformation, in excess of 3000 clones will be picked to achieve a >5 fold coverage of the human Y. This BAC library would then be used for the construction of a fine-scale map of the Y chromosome, as well as a number of other pursuits, including the identification of genes with regions of interest.