Lecture 10 - Lect 10 1 In order to understand plant life...

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Lect 10 Feb 20 2008 1 In order to understand plant life cycles, we need to have some understanding of the two types of cell division: mitosis and meiosis I. Comparison of mitosis and meiosis: overview MITOSIS MEIOSIS 1. cell divisions are not involved in gamete formation 1. cell divisions result in formation of gametes 2. direct duplication of genetic material: results in exact copies 2. reshuffling of genetic material 3. no change in chromosome number 3. reduction in chromosome number Mitosis: occurs in all eukaryots; In plants, regions of cell division; meristems In humans, new skin cells, intestinal epithelial cells mitosis: division of nucleus cytokinesis: division of cytoplasm II. The Cell Cycle Mitosis and cytokinesis are just a small part of what actually happens during cell division. In order for the two derivative cells to be just like the parent cell when they are formed, the parent cell must some how have doubled itself before it actually divided. Both doubling of cell contents and genetic material (interphase), and cell division (mitosis and cytokinesis), are part of the cell cycle. A. mitotic phase, actual separation of nucleus and cytoplasm, Occupies only 10% of time required for the complete cell cycle B. Interphase 90% of time in cell cycle, a period called interphase. Remember that the genetic material, the DNA of a cell is divided into discrete units called chromosomes. The structure of DNA: double helix of nucleic acids attached to a sugar-phosphate backbone. 1. G1 a. Just after a cell has divided, when it enters interphase, the chromosomes are highly condensed. 1 copy b. During G1 of the cell cycle, the chromosomes unfold, so they now make up part of the grey staining nucleus. organelles multiply, membrane material is synthesized 2. S- phase
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After the chromosomes unfold, they are replicated (S-phase).
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