Internet resources for phenotyping engineered rodents.

Genetically engineered mice (GEM) and rats (GER) have emerged as the main mammalian models for investigating normal (physiological, or "health") and abnormal (patho-logical, or "disease") mechanisms. Regardless of the genetic manipulation, novel GEM and GER must undergo meticulous genotypic and phenotypic analyses before it is possible to predict the significance of the engineered gene with re-spect to health and disease, especially when the desire is to extrapolate the findings to humans. Numerous websites have been generated to give researchers additional tools to facilitate genotyping and phenotyping. This list of many extant sites with descriptions of their basic features provides a starting point for new and established scientists faced with the need to characterize a new GEM or GER model.