evolutionary developmental biology

hox genes are clustered on the same chromosome, the order of the genes mirrors the order of expression along the body axis hox genes share a domain of 60 amino acids which bind to dna

vertebrates have 4 hox clusters due to 2 rounds of whole genome duplication they are expressed in a collinear fashion vertebrate hox genes also determine axial segmentation identity

homologues = characters in different organisms inherited from a common ancestor analogues = characters in different organisms similar in shape or function not due to a common ancestor

gene expression patterns problem with pleiotropy = genes expressed in many unrelated places phylogenetic relationship is crucial

anterior to posterior body axis patterning

existence of different types of eyes in various lineages of animals were considered to be a classical examples of convergent evolution pax6/eyeless and other transcription factors are necessary for development of both insects compound eyes and vertebrate lens eyes the discovery of a common regulatory network for eye development suggests the presence of proto-eyes in the common ancestor from which various eyes evolved

genes necessary for animal development found through resolution of phylogeny using molecular information

the jaw is an evolutionary novelty of Gnasthostomes jaw is a modified gill heterotopic shift of epithelial cells induce expression of patterning genes in mesenchymal interaction implicated in the evolution of jaws GF secreted by epithelial cells induce expression of patterning genes in mesenchymal cells

different groups of arthropods have different appendage organisations insects have no appendage in the abdominal region insects and crustaceans have different appendage organisations but have the same pattern of Hox gene expression drosophila Ubx sequence suppresses appendage formation whilst artemia Ubx does not the evolutions of Ubx function underlies the difference in appendage organisation