The co-ordinately controlled genes do not need to be located near each other. A domain is considered a unit of tertiary structure, while a motif is considered a unit of secondary structure. A domain refers to a discrete, locally folded unit of tertiary structure. It is assumed that domains of common structure have common functions, but not necessarily vice versa. A motif refers to a region with a particular combination of secondary structural elements such as alpha helices, beta sheets, loops, turns, etc.
Common structure implies common function.
Important tool in analysis of results from human genome project. Common structure implies common origin. There are two ways to get a collection of similar proteins 1. Antibody can be membrane bound or secreted. Fate of antibody depends on whether peptide has a stop transfer sequence or not.