EVOLUTION OF DEVELOPMENT 20.1.1 Developmental genes in diverse organisms are similar, but have different results-This discovery of a common set of developmental genes in organisms as evolutionarily distant as fruit flies and mice led to a major conclusion of evolutionary developmental biology: the amazing diversity of organisms is produced by a modest number of regulatory genes . Differences in body form result from differences in where and when these genes are turned on and off.-The transcription factors and extracellular signals that govern pattern formation in multicellular organisms , and the genes that encode them, can be thought of as a molecular tool kit , in the same sense that a few tools in a carpenter’s tool kit can be used to build many different structures. 20.2 How can mutations with large effects change only one part of the body?-embryos , like adults, are made up of modules —functional entities encompassing genes and the various signaling pathways the
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