Origin_of_Animals[1]

Origin_of_Animals[1] - Origin of Animals, Sponges &...

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Radiate Animals
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Characteristics of animals include: • Multicellular body plans • Heterotrophic nutrition by ingestion • Ability to move, at some stage, from place to place under their own power • Embryonic development from zygote to adult • Presence of flagellated cells in some stage of their life cycle Animals Arose from Single-Celled Eukaryotic Ancestors
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Animals appear to be a monophyletic group. Some homologies include: unique intercellular connections such as cytonemes and desmonemes similar embryonic stages (blastula, gastrula) shared nucleotide sequences
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Evolution of animals from ancestral Eukaryotes Oldest animal fossils are About 600 MY old Molecular evidence supports an earlier origin for animals
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Among major kingdoms, animals appear closely related to the Fungi. But the closest relatives of animals are the Choanoflagellates , a group of flagellates that form small colonies, and resemble cells found in sponges. Choanoflagellate-like cells are also found in some flatworms and rotifers. Origin of Animals Fungi Chytrids Choanoflagellates Animals
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Images of Choanoflagellates The collar region of Choanoflagellates is specialized to capture and ingest bacteria.
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Work of Nicole King (UC, Berkeley) • Uses comparative genomics • Choanoflagellates share a number of genes with animals • Genes for cell adhesion and communication • These genes are essential to multi-celled animals • The origin of these genes appears to predate their current function (an example of exaptation)
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Proterospongia intermediate between colonial flagellates and sponges • Colonial Choanoflagellate • Cells embedded in a jelly- like matrix • Differentiated into collar and amoeboid cells • Lacks internal canals (spongocoel) of sponges • Strong evidence for shared ancestry of animals and choanoflagellates
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Origin_of_Animals[1] - Origin of Animals, Sponges &...

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