At the beginning of this century genetics arose out of developmental history (Entwicklungsgeschichte) as the science of the causal understanding of development. After Spemann's epochal discovery (justifiably rewarded with the Nobel Prize in 1935) of the organizer and the beginning of the experimental analysis of developmental fields, little or no progress was made until the last few years when a virtual revolution occurred in developmental biology. If nothing else, this revolution has re-inspired in medicine an enormous respect for developmental animal models which are homologous to the human condition in the strict sense of the term, both in formal (formalgenetischer) and causal (kausalgenetischer) respects. Thus, the earliest stages of development in the primary field (during gastrulation) and in the later mosaic of secondary, epimorphic fields, represents the harmonically coordinated and epigenetically regulated effects of many genes which (with of without imprinting) code for cellular adhesion molecules, the peptide regulatory factors, homeobox genes, retinoic acid receptors and many other genes. Some of these genes act as regulators of DNA transcription, and, until recently no clinically identifiable developmental attribute to their function was known in humans. However, just in the last few weeks we have witnessed the identification of a gene on 11p13 in humans which is a paired box- and homeobox-containing gene as the cause of human aniridia, with the identical (homologous) mutation in the mouse Pax-6 gene producing the Sey phenotype (small eye).(ABSTRACT TRUNCATED AT 250 WORDS)
