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 other physical-chemical
properties of the resulting hybrid molecules. This method has enormous
potential for developmental biology. It offers a more direct approach to
the ever-present question of the genetic identity of different cell
types in an individual organism, and a more direct test of the
hypothesis of diffe- rential gene function. It offers the possibility of
localizing genes on chromosomes without the use of Mendelian genetics.
It is an indispensable tool in the isolation, purification, and
characterization of genes. This volume brings together six articles by
investigators actively working on various aspects of developmental
biology who use nucleic acid hybridization as a tool in their research.
Sound in theory, the method is in a honing phase as regards the
technical detail. This is expressed in the hesitation with which some of
the conclusions are rightly drawn.