Stereo pairs showing a three-dimensional view of in situ hybridization signals to two neighboring 
genes. DNA from the white gene (seen here in green ) and from the Notch gene ( red ) were hybrid- 
ized to the giant chromosomes from Drosophila salivary glands, fluorescently labeled, and visual- 
ized by wide-field three-dimensional optical sectioning microscopy. Top picture shows these sig- 
nals overlaid on the chromosome (blue ); bottom, the signals alone. The structure of the two genes 
is seen to be distinctly different. Scale bar = 1 fim. 
Research and photograph by Susan Parmelee in the laboratories of fohn Sedat and David 
Agard. 
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