In mice, Pax2 is expressed in eye, kidney and central nervous system. A Pax2 knockout leads to abnormalities in eye and urogenital system. Fly homeotic genes expressed to control specification of different body segments from anterior to posterior. Hox genes are truly homeotic protein coding regions. Why they do not appear as mutants in the natural population of mice and man is a puzzle awaiting resolution.
Transcriptional factors are closest to the action - genetic alterations.
Limited mutations suggest anything else is an embryonic lethal change. Would expect different functions for the three FGFRs in last stages of bone development. Current analysis is retrospective - start with human birth defects and try to establish their mechanism by relation to murine mutations or study of Drosophila genetics. It is likely that, in the future, study of developmental biology will provide clues for identification of abnormalities of human development. Most likely importance is in the less egregious, nonfatal developmental defects, such as cardiac malformations.