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24. Evolution and Phylogenies Nov 23

Science 267 1641 1643 small subunit ribosomal rna

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Unformatted text preview: small-subunit ribosomal RNA (rRNA) Proposed the clade Lophotrochozoa Found clade with molecular data, then looked for synapomorphies that could unite the clade ? ?Do they form a clade with molluscs annelids and friends - Lophotrochozoa ? Lophotrochozoa trochophore larva + lophophorates trochophore larva + lophophorates Similar analyses with 18s RNA for other major taxa established the Ecdysozoa Found clade with molecular data, then looked for synapomorphies that could unite the clade Are animals that have a cuticle and molt (mostly), copulate for reproduction another clade - the Ecdysozoa? 7 Deuterostomes Ecdysozoa Trochophore Larva OR Lophophore OR Not? Lophotrochozoa Deuterostomia Cuticle Molt Get a slightly different answer with hox genes Gerlach et al., In Silico Biol. 7, 0015 (2007); Figure 1 Most recent paper - Dunn et al. Nature 2008 posted on BB Uses Expressed Sequence Tags (ESTs) mix and match sequences of 150 genes for 77 taxa (not all genes for all taxa so used elaborate statistics to estimate trees) Final analysis used 29 Species in 21 Phyla EST is a short sub-sequence of a transcribed cDNA sequence ESTs are small pieces of DNA sequence (~200 to 500 nucleotides long) that are generated by sequencing either one or both ends of an expressed gene. The idea is to sequence bits of DNA that represent genes expressed in certain cells, tissues, or organs from different organisms and use these "tags" to fish a gene out of a portion of chromosomal DNA by matching base pairs. ESTs commonly used for gene discovery and genome mapping Relatively cheap to sequence, so generating many for many different taxa What did they get? 8 Lophotrochozoa Lophotrochozoa Ecdysozoa Ecdysozoa 9 General Results thus far: Monophyletic origin of Metazoa Arthropods are monophyletic Deuterostomia Lophophorates frequently group with Protostomes Deuterostomes always a clear group (Echinodermata, Hemichordata, Chordata) 10...
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  • Annelid, Bryozoa, Protostomes Deuterostomes Hexapoda Echinodermata Chelicerata Vertebrata Lophophores Crustacea Chordata Arthropoda Annelida Hemichordata Mollusca Other Other Nemertea pseudocoelomates pseudocoelomates Platyhelminthes Ctenophora Nematoda Cnidaria Mesozoa Pl, Placozoa Cnidaria Proto Ctenophora Sipuncula Mollusca Annelida Onychophora Arthropoda Tardigrada Bryozoa Platyhelminthes Nemertea Rotifera Gnathostomulida Chaetognatha Gastrotricha Nematoda Nematomorpha Priapulida Kinorhyncha Loricifera Phoronida Brachiop, pinnules Perivisceral pinnules

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