The informational content of cells is encoded in the nucleotide sequences of their DNA. The restrictions on base pairing- A pairing with T (U), and G pairing with C - in nature assures the fidelity of replication of DNA in cell division, and of transcription. In the test tube, these restrictions can be exploited for ascertaining similarities and dissimilarities of nucleic acids of varying origin by measuring the kinetics of reassociation of polynucleotides to double-stranded molecules in DNA- DNA renaturation or RNA-DNA hybridization experiments, and by determining the thermal stability and...

The first volume of the series, on "The Stability of the Differentiated State" received many favorable reviews from the scientific community. Many readers seem to agree with us that publication of topical volumes is a worthwhile alternative to periodic compilations of rather unrelated, though up-to-date reviews. Production of topical volumes is however, plagued with one great difficulty, that of "author synchronization." This difficulty explains the lag between volumes 1 and 2 of the series. Nevertheless we hope that the present volume will be appreciated as a valuable source of information...

~o working hypothesis amounts to much until it has been tested on suitable material. Indeed, the choice of an appropriate experimental system has often been the key to the solution of a problem. The present volume is devoted to insect imaginal disks. These groups of larval cells are the primordia of precisely characterized adult counterparts, without apparent function in larvae. At the onset of metamorphosis, the subtle interplay of hormonal signals brings growth to a halt, and differentiation begins. In the fruitfly, a host of mutations are known to affect the development of disks; these...