Pax genes contain paired domains with strong homology to genes in Droso-phila which are involved in programming early development. Pax-9, a member of the paired box-containing gene family, is closely related in its paired do-main to Pax-1. The Pax-9 gene encodes the highly conserved paired domain and the gene is a member of the same subgroup as Pax-1/undulated. Pax-9 is essential for the development of a variety of organs and skeletal elements. Mutations in either the Pax-1 or the Pax-9 genes may produce an inherited skeletal disorder such as the Jarcho-Levin syndrome or other forms of spondylocostal dysplasia, conditions resembling undulated in the mouse. A frameshift mutation within the paired domain of Pax-9 was identified in a family segregating autosomal dominant oligodontia whose members had normal primary dentition but lacked most permanent molars. In addition to lack of permanent molars, some individuals also lacked maxillary and/or mandibular second premolars, as well as mandibular central incisors. The gene which encodes Pax-9 maps to human chromosome 14q12-q13.