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Biol 121- 2010.03.29- Evolution- Great Changes, Diversity and Divergence (Ch. 27, 34).docx

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Applied Biology
APBI 200
Paul Hewitt

Biol 121 225 Freeman 556564 762767Mar 2931 10 Evolution Great Changes Diversity and Divergence 1 Mechanisms of change evolutiondevelopmental biology Evodevo small changes appear as big changes a Gene duplications and the Cambrian did gene duplications trigger the Cambrian explosion explosion Hox genes are important in specifying morphological traits and in development Homeotic genes order and place and are responsible for the 3D pattern of structureswas the increase in morphological complexity during the Cambrian bc of an increase in theand complexity of homeotic genesHypothesis new genes new bodies mutation causes new genes to arise new clusters arise as duplications increased complexity of Hox complex is related to the increased complexity of organisms Evidence there are groups that branch off early like jellyfish that have fewer Hox genes and simpler body plans conversely groups that do not branch off early have more Hox genes and more complex body plans also genes within a cluster are very similar which is perhaps due to duplicationthe whole Hox cluster could have been duplicated twice to lead to vertebrates zebrafish have 6 clusters of Hox exception crustaceans are complex but have only 5 Hox geneswhen gene duplication occurred new Hox genes were greated bc genes within the cluster are similar in structure and base sequence the entire Hox cluster was duplicated and then duplicated again in the lineage leading to vertebrates duplication of Hox genesimportant in making elaborate body plans 2 Adaptive radiation occurs when a single lineage produces many descendant species that live in a wide diversity of habitats and find food in a variety of ways eg Hawaiian honeycreepers adaptive radiations produce star phylogenies on the phylogenetic tree you can see one ancestor branching out into many different monophyletic groups adaptive radiation leads to rapid speciation and ecological diversificationthe size and shape of beaks of Hawaiian honeycreepers reflect the different feeding strategies the different seeds and leaf structures of Hawaiian silverswords reflect different moisture levels in the habitat How does adaptive radiation occur a Ecological opportunity availability of new or novel types of resources can lead to adaptive radiation adaptive radiation often occurs when habitats by unoccupied by competitors eg Anolis lizards of the Carribean the lineage includes 150 spp and there is a strong correlation bt size and shape of each spp and the habitat it occupies most Anolis species that are twigdwellers have relatively short legs and tails those that spend most of their time clinging to broad tree trunks or running on the ground have long legs and tailsb Morphological opportunity the other trigger for adaptive radiation is morphological innovationmany important diversification events in the history of life started with evolution of a key morphological trait that allowed descendants to live in new areas exploit new sources of food or move in new ways 1
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