Physical Mapping 



Localization of unique cosmid clones delineates physical landmarks on 

 chromosomes, (a) A powerful approach for constructing pfiysical maps is to 

 use fragments of fiuman DNA cloned in cosmid vectors in in situ hybridization 

 experiments with the chromosomes being mapped. These fragments can be 

 localized to specific regions (accurate to within 1 '-i of the chromosome length) 

 on human metaphase chromosomes by using computer-controlled confocal 

 laser microscopy to detect fluorescence hybridization between the fragments 

 and complementary regions on chromosomal DNA. The researcher in the 

 background is operating the microscope to produce an image on the distant 

 monitor. The researcher in the foreground is performing computer analysis on 

 the digitized hybridization data, (b) Shown in this photo is the in situ hybridization 

 of an anonymous fluorescently labeled cosmid to the long arm of human 

 chromosome 1 1 . The chromosomes are stained with propidium iodide (red), 

 and cosmid hybridization is indicated by yellow fluorescence from fluorescein. 

 The red dye on the chromosome is uniform, except at the location of in situ 

 hybridization as indicated by line /on the graphic. [Photograph b first published 

 by the American Association for the Advancement of Science in P. Lichter et al., 

 "High-Resolution Mapping of Human Chromosome 11 by in Situ Hybridization 

 with Cosmid Clones," Science 247, 64-69 (Jan. 5, 1990). Photographs a and b 

 provided by Glen Evans, The Salk Institute, and Peter Lichter. Yale University 

 Medical School.! 



22 



