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Tbx5 Gene Control

Changes in the set of genes targeted by a conserved selector gene explain the divergence of homologous structures: insect hindwings (a) and vertebrate forelimbs (b). The conserved expression of selector genes Ubx (insect hindwings) and Tbx5 (vertebrate forelimbs) indicates that ancestral forelimbs of vertebrates also expressed these genes and the ancestral hindwings of insects. While the selectors regulated certain target genes (colored boxes) in the ancestral appendage, a different set of genes came to be activated in different lineages, resulting in the evolution of morphologically and functionally divergent homologous structures in modern taxa. Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee (2001) From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design, Blackwell Publishing:Cambridge, MA, pg. 5.16, 144