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Modern Genetic Analysis Chapter 11. Applications of Recombinant DNA Technology
Introduction

In the preceding chapter, we examined the basic techniques for using recombinant DNA technology to isolate and characterize genes. In this chapter, we expand this discussion to see how having an isolated gene in hand as a DNA clone opens up diverse experimental possibilities. For example, a cloned gene can be mutated in a highly specific way in the test tube and then reintroduced into its original host to study the gene's normal functional properties. This procedure mirrors the standard genetic procedure of genetic dissection. However, in spontaneous and induced mutations, the nature of the DNA change is largely unpredictable, and the sites of the mutations can be in any number of locations within the gene. In contrast, mutagenesis in vitro can be directed toward a very specific location and type of change. Hence in vitro mutagenesis is a powerful approach to studying gene function.

The techniques of DNA cloning and restrictionenzyme analysis have been combined to create a powerful new method used in genetic mapping. In this method, the variation of restriction-enzyme target sites within a species provides large numbers of molecular "alleles," called molecular markers, for chromosome mapping. Such markers are detected by probing with cloned DNA fragments. The ability to detect such mo-lecular markers in large numbers has revolutionized mapping in most organisms, including humans.

Cloned genes (wild type or mutated) can be moved into a new host organism to create transgenic microbes, plants, and animals that could never have been made by using standard breeding procedures. This technique finds extensive use in basic research but also opens up a plethora of applications in plant and animal breeding, industrial microbiology, and medicine.

The availability of cloned genes to be used as probes also opens up new frontiers in the diagnosis of human genetic diseases in prospective parents and in fetuses in utero.

First, we examine some ways in which specific mutations can be made in cloned genes in the test tube (in vitro); in other words, how to fabricate "designer genes."

© 1999 by W. H. Freeman and Company. All rights reserved.