The obese gene is expressed in lean littermates of the genetically obese mouse (C57BL/6J ob/ob)

Some individuals of the mixed group of "lean" littermates (+/ob and +/+) of (C57BL/6J ob/ob) often suggest phenotypic characteristics of ob/ob animals. Therefore, it was of interest to determine whether expression of the ob ge ne had physiological significance in +/ob animals. Body weight (BW),:fastin g blood glucose (FBG), and body core temperature (T-r) were monitored betwe en 62 and 364 days of age in +/+ and +/ob mice. Among females but not males , +/ob mice were heavier (P = 0.003) and FBG levels were greater (P = 0.04) than in +/+ animals. Comparison of T-r indicated differences suggesting fa lling T-r in +/ob but rising T-r in +/+ mice with age in males but not fema les. Multivariate analysis of variance yielded genotype effects for both ma les (P = .0.002) and females (P = 0.02). BW, FBG, and T-r alone were suffic ient at the 75% level for genotypic characterization and separation of +/? animals as +/ob or +/+; clearly expression of the ob,:gene in heterozygotes of the +/ob animal may make the mixed +/? group inappropriate as lean cont rols.