A HIGH-RESOLUTION PHYSICAL MAP OF 2.5-MBP OF THE DOWN-SYNDROME REGIONON CHROMOSOME-21

The region surrounding D21S55 in band 21q22 of human chromosome 21 has been implicated in the etiology of Down syndrome (DS). In this paper, we report the construction of a high resolution map of a 2.5 Mb regio n around the marker D21S55. Characterization of YAC clones by accurate size determination, end isolation and marker assignment was used to b uild a refined YAC-based map. The YAC clones were then used to isolate 284 cosmid clones, covering 2.3 Mb, from a chromosome 21-specific cos mid library. The cosmid clones were ordered into overlapping groups an d a restriction map of each group was determined. The groups of cosmid s were then ordered and oriented with respect to the YAC-based map. Th is high resolution map provides the framework for further analysis of the region by transcribed sequence mapping and sequence determination.