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| Modern Genetic Analysis Chapter 10. Recombinant DNA Technology Cloning a Specific Gene Figure 10-10. Facing page: (a) A genomic library can be made by cloning genes in l bacteriophages. When a lawn of bacteria on a petri plate is infected by a large number of different hybrid phages, each plaque in the lawn is inhabited by a single clone of phages descended from the original infecting phage. Each clone carries a different fragment of cellular DNA. The problem now is to identify the clone carrying a particular gene of interest (dark blue) by probing the clones with DNA or RNA known to be related to the desired gene. (b) The plaque pattern is transferred to a nitrocellulose filter, and the phage protein is dissolved, leaving the recombinant DNA, which is then denatured so that it will stick to the filter. The filter is incubated with a radioactively labeled probe; that is, a DNA copy of the messenger RNA representing the desired gene. The probe hybridizes with any recombinant DNA incorporating a matching DNA sequence, and the position of the clone having the DNA is revealed by autoradiography. Now the desired clone can be selected from the culture medium and transferred to a fresh bacterial host, so that a pure gene can be manufactured. (After R. A. Weinberg, "A Molecular Basis of Cancer," and P. Leder, "The Genetics of Antibody Diversity." Copyright © 1983, 1982 by Scientific American, Inc. All rights reserved.)

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