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Lec9notescomplete - Bio1A Chapter 12 The Cell Cycle Lecture...

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Bio1A Lecture 9 Complete 1 Chapter 12 The Cell Cycle Cell Division * The ability of organisms to reproduce best distinguishes living things from nonliving matter * The continuity of life is based upon the reproduction of cells, or cell division Why Divide? * In unicellular organisms, division of one cell reproduces the entire organism * Multicellular organisms depend on mitosis , cell division, for: * Development from a fertilized cell * Growth * Repair * Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division Fig. 12-2 Mitosis makes clones: identical daughter cells * Cells duplicate their genetic material before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA * A dividing cell duplicates its DNA, allocates the two copies to opposite ends of the cell, and only then splits into daughter cells Cellular Organization of the Genetic Material * A cell’s endowment of DNA (its genetic information ) is called its genome * DNA molecules in a cell is associated with proteins. The proteins help organize and fold the DNA into condensed form to facilitate distribution of genetic material between the daughter nuclei. * Chromatin = DNA and protein in the unfolded, not condensed, not compact form. * Chromosomes = DNA and protein in the folded, condensed and most compact form. Somatic cells vs. Gametes * Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus * Somatic (nonreproductive) cells have two sets of chromosomes. They are diploid (2n) . * Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells. They are haploid (n) Fig. 12-3 Distribution of Chromosomes During Cell Division * In preparation for cell division, DNA is replicated and the chromosomes condense * Each duplicated chromosome has two sister chromatids , which separate during cell division * The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached.
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Bio1A Lecture 9 Complete 2 Counting chromosomes * By convention, to figure out how many chromosomes there are count the
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Lec9notescomplete - Bio1A Chapter 12 The Cell Cycle Lecture...

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