ZOO 3050 Lecture Notes - Lecture 2: Spindle Apparatus, Polyspermy, Germ Cell
13 Apr 2018
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Document Summary
Major component of a sexual life cycle: cleavage, multiple rounds of mitosis. All cells are mostly identical to each other, eventually activate genome for specialization: gastrulation, cells move into specific layers. Germ layers will form specific structures: larval development to metamorphosis is an indirect life cycle. Metamorphosis dramatically changes in appearance: reproductive adult, ability to sexually reproduce. Cleavage patterns are diverse: series of rapid mitotic divisions, blastomeres = cytoplasm divided into smaller cells, no change in size-division into thousands of cells, blastula=many blastomeres that open up blastocoel, different form in different animals. In sea urchin unequal cleavage after 3rd division: micromeres, mesomeres, macromeres. Cleavage is either holoblastic or meroblastic: holoblastic, complete cytokinesis (cell cleavage) with each cell division, meroblastic i. e. sea urchins, mammals, amphibians. Incomplete cytokinesis: cytoplasmic continuity maintained for many cell cycles (spermatogenesis, cleavage furrow does not completely divide mother cell into 2 daughter cells i. e. fish, birds, most insects.
