BIS2C_Lect26_Ward_Development___Sponges_ppt

BIS2C_Lect26_Ward_Development___Sponges_ppt - BIS2C Winter...

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1 BIS2C Winter 2012 (Ward) Lecture 26. Animal development (cont’d) & Sponges Today’s lecture (29 February) animal development sponges (Porifera) Friday’s lecture Animal Development Zygote Blastula Gastrula Cleavage : early stages of cell division after zygote formation, resulting in multiple cells (blastomeres) and establishment of a longitudinal axis (animal-vegetal axis) Animal Development Cleavage : early stages of cell division after zygote formation Patterns of cleavage vary among different animal groups, especially as a function of how much yolk (stored nutrient) is in the egg. Animal Development In invertebrates we can distinguish two fundamental kinds of cleavage: radial cleavage and spiral cleavage . Cleavage : early stages of cell division after zygote formation Radial cleavage : cells divide parallel to, or at 90° to, the animal- vegetal axis, and accumulate in even, symmetrical layers Animal Development Spiral cleavage : cells divide at an oblique angle to the animal- vegetal axis, and new cells lies in furrows between existing ones Animations available at: http://learning.ucdavis.edu/DevBio/ Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Animal Development
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2 Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Diploblastic animals: two cell layers formed, ectoderm and endoderm Animal Development Animal Development Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Triploblastic animals: three cell layers formed, ectoderm , endoderm and mesoderm blastula blastula ? diploblasty gastrula blastula ? diploblasty gastrula triploblasty
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3 Clicker Question 1. Which of the following statements is false ? a Animals exhibiting a blastula stage of development a. Animals exhibiting a blastula stage of development form a monophyletic group. b. Animals exhibiting a gastrula stage of development form a paraphyletic group. c. Animals with diploblastic development form a paraphyletic group. d. Animals with triploblastic development are a clade. Major lineages of metazoans, according to older (8 th ) edition of Life Sponges (Porifera) The older edition of your textbook ( Life, 8 th Edition ) treated sponges as a paraphyletic group comprising three clades: 1. glass sponges (Hexactinellida) 2. demosponges (Demospongiae) 3. calcareous sponges (Calcarea) Wh t ld thi t b t th f t b d i What would this suggest about the features observed in sponges?
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4 Clicker Question 2. Pick the best answer. Based on the phylogeny presented in the older edition of
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BIS2C_Lect26_Ward_Development___Sponges_ppt - BIS2C Winter...

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