Ch31 Animal Origins - 31 Animal Origins and the Evolution...

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31 Animal Origins and the Evolution of Body Plans
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31 Animal Origins and the Evolution of Body Plans 31.1 What Characteristics Distinguish the Animals? 31.2 What Are the Features of Animal Body Plans? 31.3 How Do Animals Get Their Food? 31.4 How Do Life Cycles Differ among Animals? 31.5 What Are the Major Groups of Animals?
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31.1 What Characteristics Distinguish the Animals? Traits that distinguish the animals: All are multicellular ; and undergo development from a single cell All are heterotrophs Have internal digestion processes Most can move; have specialized muscle tissues
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31.1 What Characteristics Distinguish the Animals? The animals are monophyletic . Evidence from gene sequencing supports this. Morphological synapomorphies : Unique cell junctions: tight junctions, desmosomes, and gap junctions Extracellular matrix molecules, including collagen and proteoglycans
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31.1 What Characteristics Distinguish the Animals? Animals also have similar organization and function of Hox genes and other developmental genes. The common ancestor of animals was probably a colonial flagellated protist, similar to choanoflagellates.
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How Does Gene Expression Determine Pattern Formation? Hox genes are expressed in different combinations along the length of the embryo; they determine what each segment will become. Hox genes map on chromosome 3 in Drosophila, in two clusters, in the same order as the segments whose functions they determine.
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Figure 19.19 Hox Genes in Drosophila
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Hox Gene Expression Determines Pattern Formation All the hox genes have a common DNA sequence and probably arose from a single gene in an unsegmented ancestor. The common 180-base pair sequence is called the homeobox . It encodes a transcription factor that binds DNA— called the homeodomain . These transcription factors regulate development in animals as diverse as flies and humans.
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Figure 31.1 The Phylogeny of Animals
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31.1 What Characteristics Distinguish the Animals? Functional specialization of cells in the choanoflagellate colony arose; and cells continued to differentiate. Coordination among groups of cells may have been improved by regulatory molecules; eventually leading to larger, more complex animals.
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31.1 What Characteristics Distinguish the Animals? Clues to evolutionary relationships among animal groups are found in fossils, patterns of embryonic development, morphology and physiology, protein structure, and gene sequences.
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Patterns of embryonic development have provided many clues to animal phylogeny. Cleavage : The first few divisions of a zygote. Several cleavage patterns distinguish animal groups. The patterns are influenced by
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This note was uploaded on 03/30/2011 for the course MATHMATICS 1101 taught by Professor Zhong during the Spring '11 term at Georgia State.

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Ch31 Animal Origins - 31 Animal Origins and the Evolution...

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