These Ihhfl/fl mutant mice possess loxP sites flanking exon 1 of the Indian hedgehog (Ihh) gene. IHH is involved in growth plate maintenance and sustaining trabecular bone after birth. It is also essential for chondrocyte proliferation and differentiation, and osteoblast differentiation during prenatal endochondral bone formation. Mice that are homozygous for this allele are viable and fertile. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have exon 1 deleted in the cre-expressing tissues. For example, when bred to FVB-Tg(Col2a1-cre/ERT)KA3Smac/J mice (Stock No. 006774), tamoxifen induction resulted in IHH deficient mice which exhibited complete loss of the growth plate and the articular surface, leading to loss of the primary spongiosa, and to impaired bone growth after birth.