Table 1  Distribution of Cftr genotypes in female offspring from breeding Cftr heterozygotes on the B6 and mixed backgrounds.
B6 Background  Mixed Background
Cftr  Observed  Expected  Observed  Expected
+/+  207  175  57  47
+/-  371  350  88  94
-/-  122  175  42  47
P  0.00001 (0.04533)*   0.21724
Statistical analysis was by Chi-square. (*) P-value if the sample size for the B6 mice is adjusted to be equal to that of the mixed background mice, assuming the same distribution of genotypes.
Table 2  Distribution of Cftr genotypes in male offspring from breeding Cftr heterozygotes on the B6 and mixed backgrounds.
B6 Background  Mixed Background
Cftr  Observed  Expected  Observed  Expected
+/+  240  201  57  52
+/-  431  403  115  104
-/-  134  201  36  52
P  <0.00001 (0.01612)*   0.03749
Statistical analysis was by Chi-square. (*) P-value if the sample size for the B6 mice is adjusted to be equal to that of the mixed background mice, assuming the same distribution of genotypes. The major cause of death in CF mice is intestinal obstruction, and intestinal obstruction is worsened when the mice are fed standard solid mouse chow [35].