Biologists ask how the growth, development and behaviour of organisms happen, how these processes are co-ordinated and how they are regulated by the environment. Today the questions are phrased in terms of the genes involved, their structure and the control of their expression. Mutations (recognised by a change in phenotype) label genes and can be used to study gene structure, gene function and the organisation of the genome. This is Genetics . Study of phenotypes down to the level of the enzymes and structural proteins coded for by genes is Biochemistry . It is self evident that only by studying phenotype ( Biochemistry ) can we do Ge netics and that Genetics (perturbation of the phenotype) is the key to understanding the Biochemistry . There can surely be no better argu ments for a more holistic approach to biology than the massive output of knowledge from microbial Biochemical Genetics and the more recent revelations from Molecular Genetic studies of development in Droso phila.