Effect of genetic background on body weights of CF mice. (A) Female and (B) male mice were weighed at 4 and 8 weeks of age. Data are means ± SEM. (*) P < 0.001 vs other three groups by ANOVA with a post-hoc Tukey's test. There were no significant differences for any of the other comparisons. Data were obtained from: 65 wild type and 26 CF B6 females, 36 wild type and 8 CF mixed background females, 68 wild type and 30 CF B6 males, and 37 wild type and 6 CF mixed background males.