Chapter Outlines - Chapter Outlines 2.1 Cell Structure Is...

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Chapter Outlines 2.1 Cell Structure Is Closely Tied to Genetic Function In eukaryotes, transmission of genetic material from one generation of cells to the next involves mitosis and meiosis. Meiosis leads to production of gametes or spores. Mitosis leads to production of two cells, each with the same  number of chromosomes as the parent cell. In eukaryotes, DNA resides in the nucleus and organelles reside in the cytoplasm (Figure 2-1). Cytoplasm consists of a colloidal material called the cytosol, which surrounds and encompasses the cellular  organelles. The cytoskeleton, consisting primarily of tubulin-derived microtubules and actin-derived microfilaments, provides a  lattice of support structures within the cytoplasm. Other important organelles include chloroplasts (found only in plants, algae,  and some protozoans), the endoplasmic reticulum (ER), and mitochondria. The cell is surrounded by a plasma membrane. Plant and bacterial cells also have a cell wall composed mainly of  cellulose and peptidoglycan, respectively. DNA in the nucleus is complexed with an array of acidic and basis proteins into thin fibers. During nondivisional  phases of the cell cycle, these fibers are uncoiled and dispersed into chromatin. Chromatin fibers coil and condense to form  chromosomes during mitosis and meiosis. Centrioles in the cytoplasm, located in a specialized region called the centrosome, organize spindle fibers for  movement of chromosomes during meiosis and mitosis. 2.2 Chromosomes Exist in Homologous Pairs in Diploid Organisms Early in meiosis, homologous chromosomes form pairs, or synapse. In each homologous pair of chromosomes, one  member is derived from each parent. Each synapsed structure is initially called a bivalent, which eventually gives rise to a unit, the tetrad, consisting of four  chromatids. Each diploid organism contains two copies of each gene. The members of each pair of genes need not be identical.  Alternative forms of the same gene are called alleles. Meiosis converts the diploid number (2n) of chromosomes to the haploid number (n). Gametes contain a haploid set of chromosomes. Fusion of two gametes at fertilization results in a diploid zygote. Sex-determining chromosomes are usually not homologous (Figure 2-4) yet behave as homologs in meiosis. 2.3 Mitosis Partitions Chromosomes in Dividing Cells Genetic material is partitioned to daughter cells during nuclear division (karyokinesis). Cytoplasmic division  (cytokinesis) follows.
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