Chapter 7 General Recombination

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Genetic recombination was first demonstrated in bacteriophages with phage T2 of Escherichia coli (Delbruck and Bailey, 1946; Hershey, 1946), and shortly thereafter with phage λ as well (Jacob and Wollman, 1954). It was soon apparent that recombination in phage can be analyzed according to general principles of breeding analysis developed for higher organisms, although the special kinetics of phage growth require in addition a population genetic analysis (Visconti and Delbruck, 1953). Recombination in phage may be a useful model for recombination in general (see, for example, Davern, 1971), and because of the ease with which they can be manipulated, phage systems seem at present to be the best material for studying recombination at the molecular level. General recombination in λ has been approached from three directions. First, studies of molecular chemistry in crosses with isotopically labeled phages have shown that recombination can occur by breaking and joining of parental molecules, and that extensive DNA synthesis may be involved but seems not to be essential. Second, formal genetic analysis has shown that the recombination joint includes a heteroduplex overlap of DNA from the two parents, in which on the average several genetic exchanges are clustered tightly. Third, classical techniques of biochemical genetics have identified some of the genes and enzymes involved. Although our understanding of recombination is still rudimentary, recent developments in λ have been encouraging. The three areas—genes and enzymes, molecular chemistry, and formal genetics—will be discussed in turn, and the chapter will close with a brief discussion...