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CH 10: Cell Division (p.240) 10-2: Cell Division (p.244) In unicellular organisms, cell division via mitosis is a form of asexual reproduction In multicellular organisms cell division is a source of new cells for (a) growth & (b) repair Triggered by growth factors: chemical signals released by ther cells Chromosomes o Chromatin condenses into visible chromosomes during cell division o Prokaryotes usually have 1 simple, circular chromosome of DNA o Eukaryotes have multiple complex, rod-shaped chromosomes Consist of DNA wrapped around proteins called histones (fig 12-10) Chromosomes replicate before cell division into 2 identical sister chromatids attached at centromere (fig 10-3) Cell Cycle – series of events a cell goes thru as it grows & divides (fig 10-4) o 4 phases: a. G1 – period of normal growth b. S – DNA replication (synthesis) c. G2 – growth & prep for division d. M – mitosis & cytokinesis I. Interphase (G1, S, G2 phases) – period of cell growth btwn divisions II. Mitosis – division of nucleus (P-M-A-T) (fig 10-5) o Prophase chromosomes become visible Centrioles move to opposite ends of the cell & form the spindle which lines up and separates chromosomes Nucleolus disappears & nuclear envelope breaks down o Metaphase –chromosomes line up in middle of cell o Anaphase – sister chromatids are separated & pulled to opposite poles chromatids become separate chromosomes o Telophase – chromosomes uncoil Nuclear envelope & nucleolus reappear in each daughter cell III. Cytokinesis – division of cytoplasm o Cell membrane pinches to separate animal cells o Cell plate (cell wall) forms in plant cells o Results in 2 identical daughter cells 10-3: Regulating the Cell Cycle (p.250) Density-dependent inhibition: cells stop dividing when crowded (fig 10-7) Cancer: disorder in which cells do not respond to normal cell cycle regulation o caused by exposure to carcinogens o cells divide uncontrollably & form tumors Benign tumors are harmless (“benign is nice”) Malignant tumors are harmful & spread to other tissues in a process called metastasis o Some types of cancer: Carcinoma/melanoma: skin or tissues lining organs Sarcoma: connective tissues (bone, cartilage, fat, muscle, blood, etc.) Leukemia: white blood cells, blood-forming tissue (bone marrow) Lymphoma: lymph nodes, spleen, or bone marrow Prophase Metaphase Anaphase Telophase Date: 11-4: Meiosis (p.275) Chromosome Number o Homologous chromosomes: pair of chromosomes that have genes for the same traits 1 of each pair comes from each parent Gene: a section of DNA that codes for a specific trait o Somatic cells are diploid (2N): they contain 2 sets of chromosomes in homologous pairs Diploid number for humans is 46 (2N = 46) o Gamete: sex cell (sperm or egg) Haploid (N): contains only 1 set of chromosomes Haploid number for humans is 23 (N = 23) Meiosis: form of cell division that forms 4 gametes for sexual reproduction (fig 11-15) o Meiosis I Homologous chromosomes pair up to form tetrads during prophase I Crossing-over occurs when homologous chromosomes exchange portions of their chromatids (fig 11-16) - Recombination increases genetic diversity in offspring Homologous chromosomes line up in pairs & separate to form 2 haploid (N) cells Sister chromatids do NOT separate o Meiosis II Sister chromatids separate Results in 4 haploid (N) daughter cells (NOT identical!) Independent Assortment: chromosomes line up randomly & separate independently from one another o Increases genetic diversity in offspring Fertilization occurs when a haploid sperm & egg join to form a diploid zygote (N + N = 2N) CH 14: The Human Genome (p.340) Date: 14-1: Karyotypes and Chromosomal Disorders (p. 341) Genome: all of a cell’s DNA Karyotype: picture of chromosomes arranged in order o Karyotypes of human somatic cells contain 2 sets of 23 chromosomes (23 pairs) Sex chromosomes - determine sex/gender o XX = female ; XY = male All other chromosomes are autosomes (22 pairs) Gametes have 22 autosomes & 1 sex chromosome o All egg cells have 1 X; sperm have either X or Y (50/50) (fig 14-2) 14-2: Human Chromosomes (p.349) Nondisjunction occurs when homologous chromosomes do NOT separate during meiosis (fig 14-15) o Leads to chromosomal disorders Trisomy: having an extra chromosome (3 homologous chromosomes instead of 2) Monosomy: missing a chromosome - Ex: Down syndrome (trisomy 21) 3 copies of chromosome 21 - Ex: Turner’s syndrome – females w/ only one X (45,X) sterile * Y determines sex of individual --> XXX (Triplo-X / trisomy X) – fertile, normal intel); XYY – antisocial, fertile