In this section, we discuss three examples of research studies that have identified a gene in an animal model and then studied the same gene in humans. The same polymorphisms are not expected to exist in both mice and humans. Instead, the unit of translation is the gene, about 99% of which have reasonably cleared human homologs. The assumptions of this approach include: (1) that genes have similar functions with respect to complex traits in mice and humans, (2) that these effects are reasonably robust to genetic context (strain background in mice, and genetic diversity in humans), (3) environmental factors will not confound mouse and human studies and (4) only a small fraction of the genes in the genome have the ability to modulate the sorts of traits that we are interested in studying. The final assumption is important because this discovery of genes using mouse studies will be most valuable if the total number of genes that influence a given trait is small, so that identifying such genes is significantly better than arbitrarily selecting a gene. If these assumptions are substantially incorrect then this approach will not be very productive.
