6 - Biology 1001 Spring 2008 (B. Fall), Class notes, topic...

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Biology 1001 Spring 2008 (B. Fall), Class notes, topic #6—Mitosis, meiosis Preparation: complete the reading assignment in your text (Freeman, Biological Science, 2 nd ed.): pp. 227- 237, 248-260, 263. I also strongly recommend that you work through two tutorials on the Freeman companion website and CD that are referenced below in the outline, part V.-A.: (Phases of mitosis; Meiosis). These are also on the WebVista webpage for class 6. Learning objectives: 1. Outline the basic sequence of events of mitosis. 2. Outline the basic sequence of events of meiosis. 3. Appreciate similarities and differences of mitosis and meiosis, including the outcome of each process. 4. Understand the meaning of homologous chromosomes and sister chromatids, the difference between them, and their origins. 5. Relate the events of meiosis to the results of Mendel’s breeding experiments with peas. Notes: I. Introduction : cell division A. In prokaryotes (all unicellular), cell division (asexual reproduction) occurs by the process of binary fission (not mitosis). Prokaryotic DNA is in the form of a single circular (i.e., joined) chromosome. B. In eukaryotes, there are two types of nuclear division: mitosis and meiosis. Mitosis results in two new nuclei with the same number of chromosomes as the original, with the same genetic composition. Mitosis is important in growth of multicelled organisms, and replacement of damaged or dead cells. In contrast, meiosis results in halving of the number of chromosomes in a diploid cell, ultimately producing four haploid cells (gametes) with half the chromosome number of the parent cell. II. Cell cycle in eukaryotes refers to the life cycle of a cell, from its formation until it completes division. The cell cycle consists of interphase (“between phases”) with three stages (G 1 , S, G 2 ) followed by mitosis ( the dividing phase ) , with five stages. The stages are a continuum rather than discrete. Mitosis itself comprises a relatively short part of the cell cycle; most time is spent in interphase. A. Cell cycle stages (mnemonic: IPPMAT): 1. Interphase (replication of chromosomes (DNA synthesis) occurs during S stage); precedes mitosis. DNA replication results in each chromosome having two genetically identical units, called sister (or twin) chromatids . Thus in cells entering mitosis (as well as meiosis), each chromosome has already been duplicated 2. Prophase (the first of five stages of mitosis proper)—chromosomes (each consisting of sister chromatids) condense; centrosomes (in animal cells) move toward poles, and mitotic spindle
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This note was uploaded on 04/21/2008 for the course BIOL 1001 taught by Professor Fall during the Spring '08 term at Minnesota.

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6 - Biology 1001 Spring 2008 (B. Fall), Class notes, topic...

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