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DNA and Cell Division

DNA and Cell Division. Packaging of DNA. DNA segments are coiled around histones forming a complex called a nucleosome Non-dividing cells DNA is loosely coiled forming network called chromatin Cells preparing to divide

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DNA and Cell Division

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  1. DNA and Cell Division

  2. Packaging of DNA • DNA segments are coiled around histones forming a complex called a nucleosome • Non-dividing cells • DNA is loosely coiled forming network called chromatin • Cells preparing to divide • DNA becomes tightly coiled forming distinct structures called chromosomes

  3. Chromosomes • Human somatic cells contain 46 chromosomes that exist as 23 pairs of homologous chromosomes • Homologous chromosomes: same size and shape

  4. Homologous Chromosomes • Code for the same traits • Cells contain two genes for every trait

  5. Cell Cycle • Period of time from cell formation to cell division • Phases: • Interphase • Period of cell growth • Mitotic phase • Cell division

  6. Mitosis • One cell divides into 2 daughter cells with identical copies of DNA • Functions of mitosis • embryonic development • tissue growth • replacement of dead cells • repair of injured tissues

  7. Phases of Mitosis • Prophase • Metaphase • Anaphase • Telophase

  8. Prophase • Chromatin condenses into chromosomes • Spindle fibers grow from centrioles

  9. Metaphase • Chromosomes line up along equator of cell • Spindle fibers attach to chromosomes

  10. Anaphase • Spindle fibers separate sister chromatids • Daughter chromosomes move towards opposite poles of cells

  11. Telophase • New nuclear envelopes assemble around each set of daughter chromosomes • Chromosomes uncoil into chromatin

  12. Cytokinesis • Division of cytoplasm into 2 cells • Myosin pulls on microfilaments of actin in the membrane cytoskeleton (animal cells) • creates crease around cell equator called “cleavage furrow”  Cell pinches in two

  13. Sexual Reproduction • Genetic material from two parents are combined to form a unique combination of genes

  14. Meiosis • Unique type of cell division that reduces chromosome number by half • Produces gametes or sex cells • Spermatogenesis  sperm cell production • Oogenesis  egg cell production

  15. Gametes • Male and female gametes (sex cells) combine genetic material to form a fertilized egg (zygote) containing 46 chromosomes

  16. Formation of Gametes • Gametes contain a single copy of 23 chromosomes (haploid) • Requires two cell divisions  Meiosis • Meiosis I separates homologous chromosome pairs into two haploid cells • Meiosis II separates duplicated sister chromatids into four haploid cells

  17. Crossing Over

  18. Independent Assortment

  19. Errors in Meiosis Polypoid gamete Contains extra complete sets of chromosomes Nondisjunction Replicated chromosomes fail to separate

  20. Prokaryotic Cell Division • Asexual Reproduction • Daughter cells are genetically identical to parent cell

  21. Genetic Variability in Asexual Reproduction • Transformation • Transduction • Conjugation • Mutations

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