Fig. 6. Analysis of chondrocyte proliferation in ß-catenin and Ptch1 mutant embryos. (A) BrdU-labelled cells were detected by immunohistochemistry on sections of the developing tibia at 14.5 dpc. Zone I (resting zone) contains slow proliferating chondrocytes and Zone II (proliferative zone) contains fast proliferating chondrocytes. For each genotype, BrdU-labelled and total chondrocyte numbers in the boxed regions were counted from three different samples to find the mean. (B) Comparison of BrdU-labelled chondrocytes in Zone I and II in different mutants. Three samples were counted, and the mean±s.d. and statistically significant P-values are shown.