Schematic representation of the physical linkage of murine Irxgenes in two clusters on mouse chromosomes 13 (A) and 8 (B). The top half of the figure shows the generation of YAC contigs based on polymerase-chain-reaction (PCR)-screening of the large MIT mouse YAC library (WI/MIT 820). Squares indicate the relative positions of murine Irx genes. Single YAC clones are represented as horizontal lines. The name of each clone is indicated. The bottom half represents database information for individual YAC clones provided by the Whitehead Institute/MIT Center for Genome Research (WI/MIT CGR). Underneath individual genomic marker (sequence-tagged sites; open circles) assigned to YAC clones considered by WI/MIT CGR database are shown. Genomic markers D8Mit147, D8Mit309 and 20.MMHAP88FRG8.seq were also tested by PCR. Details on each marker/YAC clone are available on the World Wide Web site at the WI/MIT CGR (http://carbon.wi.mit.edu:8000/cgi-bin/mouse/index).