Segments of YAC contig 2 and of the underlying bacterial clone contig (Chr_Xctg3). The image is taken from the graphical display of the contig assembly program SAM. Landmarks are shown at top, with clone ends (YAC or PAC) in yellow and other STSs in blue–green. YACs are named according to Fig. 2; PACs are prefixed dJ (RPCI1, RPCI3, RPCI4, and RPCI5) or dA (RPCI6); and BACs, bA (RPCI11). Dark blue boxes indicate strong positive landmark–clone associations; and pale gray, weak associations; a yellow box indicates the end of the YAC or PAC clone from which a probe or STS was derived; green boxes show cases in which bacterial clones have not been screened for the relevant markers.