Over the past twenty years, the disciplines of cellular and molecular biology have generated a bounty of information pertaining to the understanding of the structure and function of eukaryotic cells . It is now recognized that individual cells regulate their activities in response to a multitude of external signals ; that external signals, a- ing through a limited number of second messenger systems, modulate the cell''s pattern of gene expression; and that the cohort of genes available for regulation is dependent upon the developmental history of the cell. Extrapolating these truths to the whole organism is a challenge that has been met by an increasing number of investigators . The wealth of information that molecular and cell biology has provided us with is now being integrated into an understanding of whole t- sues, organs, and organisms. Without such an integration, the molecular information will be nothing more than a confusing catalog of sequences and structures. Central to this project will be the app- cation of the powerful new techniques described in Transgenesis Techniques: Principles and Protocols .
