Evolutionary analysis of genes involved in early embryonic pattern formation in Drosophila

Segmentation and homeotic genes have originally been identified and analyzed in Drosophila. Molecular techniques such as low stringency hybridization or PCR now allow to clone homologs of these genes from different organisms. This provides a basis to study the evolution of pattern formation mechanisms between organisms at the gene level, creating a new discipline: molecular comparative embryology. This chapter discusses the practical and conceptual problems arising from this approach.