A HIGH-FIDELITY PHYSICAL MAP OF HUMAN-CHROMOSOME 21Q IN YEAST ARTIFICIAL CHROMOSOMES

Understanding of the human genome has been advanced significantly by t he development of large DNA fragment libraries. To create a map of chr omosome 21q that integrates the physical, cytogenetic, and linkage map s, we have characterized a subset of 127 chromosome 21 yeast artificia l chromosome (YAC) clones for size, by pulsed field gel electrophoresi s, for chimerism and cytogenetic location, by fluorescence in situ hyb ridization (FISH), and for sequence-tagged sites (STS) content, by PCR . It was found that 54% generated unique map locations on chromosome 2 1, and 45% detected sites on other chromosomes, of which 33% likely re presented true chimerism. Using a simple algorithm, the data from nonc himeric clones have been combined to generate a size-corrected minimal tiling pathway including 58 chromosome 21q YACs that represent simila r to 33 Mb and include 9 gaps. To confirm the resulting order and rela tionship to the cytogenetic map, the breakpoints from 23 cell lines pa rtially aneuploid for chromosome 21 have been analyzed by quantitative Southern blot dosage analysis and FISH with a subset of the markers. As one way of investigating the relationship of the genetic to the phy sical map, the genetic map was superimposed on the physical map using a subset of well-defined markers common to both. The results suggest p otential hot spots for recombination and/or gaps in the physical map. This integrated map will facilitate the search for the genes responsib le for the Down syndrome phenotypes and provide a better understanding of genome organization and chromosome structure.