Bone defects inCbfb^rss/rss and Cbfb^rss/− fetuses. (A) Alcian blue– and alizarin red–stained skeletal preparations from postnatal day 0.5 Cbfb^+/+ and Cbfb^rss/rss fetuses. Cartilaginous skeleton is blue and ossified bone is pink. Areas of skeletal abnormalities are indicated with arrows. (B) Tibias from 17.5-dpc Cbfb^+/+, Cbfb^rss/rss, and Cbfb^rss/− fetuses stained for cartilage with safranin O (red) and for osteoblasts and hypertrophic chondrocytes by virtue of their alkaline phosphatase activity (blue). hc indicates hypertrophic chondrocytes; d, diaphysis; and so, secondary ossification center.