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.