Gene synthesis
Simple Genes
Complex Genes
Gene Clusters

Genetic bits and parts, genetic modules:

Repositories of standardized genetic elements are seen as one prerequisite to driving developments in metabolic engineering and synthetic biology in general. These elements, whether they are promoters, enhancers, coding regions, recombination signals, etc., need to be modular in nature and compatible with a basic design as this avoids unnecessary cloning steps and guarantees compatibility at all levels.
Any design will impose certain constraints on the gene's make-up. One just needs to make sure to preserve maximum flexibility within these design parameters that will accomodate genes from other (cloning or expression) systems as well.