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Unformatted text preview: 1 2009 BIO153: Lecture 5 Development in Evolution January 19th, 2009 Topics: • role of development in macroevolution and the generation of diversity • differential gene expression and transcription factors • the animal “toolkit” Development has an important role in macroevolution • evolutionary change in morphology, function, organization & performance of the organism involves development • the study of development helps answer the question: how do diverse descendents arise from a common ancestor? Development and diversity: 1. Changes in developmental processes result in the changes in phenotype seen in diversification in a lineage • especially evident in adaptive radiations (rapid speciation within a lineage; usually as the result of colonization of a new environment with several vacant niches) • e.g. Hawaiian honeycreepers; cichlid fish in Africa; Heliconius butterflies 2. Shared developmental pathways show relatedness • lineages descended from an ancestor evolve in similar ways because they share an inherited developmental pathway ( parallelism ) 2 • e.g. within the frog and salamander lineages, both show digit reduction in forelimb (5 → 4) • in frogs: first digit is lost; in salamanders, 5 th digit is lost • frogs share a particular developmental mechanism through inheritance; salamanders share another mechanism • thus, same result (digit loss) is achieved through 2 different pathways conserved by the 2 lineages (frogs and salamanders diverged ~135 million years ago (Mya)) 3. Development puts constraints on the types of variants possible: • natural selection can only act on the array of variants that are produced • developmental pathways are complex and integrated; thus, certain variations in phenotype are simply not possible (viable) • e.g., the wings of winged tetrapods are modified forelimbs; a winged horse would have to be built through the duplication of the forelimb; this is not viable in embryonic development; thus Pegasus is not possible! Process of development: how do we go from a single cell to an adult?...
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