Approximately two equal-sized segments of the small intestine were pooled per animal: one taken from the proximal jejunum and one from the distal ileum. We did generate a second data set (not in GeneNetwork) for different segments of the the GI tract from stomach to distal colon for C57BL/6J and DBA/2J parental strains. These additional data are available upon request from Drs. Dennis Black and Lu Lu.