CELL DEVIATION

• Cell Cycle


  The sequence of growth and division of a cell
• Phases of Interphase

  • G1
  • S
  • G2
• Interphase


  • Cell grows, and the organelles double prior to the actual splitting of the nucleus
  • 93% of a cell's life is spent in interphase
• G1 phase


  1. Organelles double

  2. Each new cell needs a complete set of organelles
• S phase

  1. DNA is replicated

  2. Each cell needs a complete and identical set of DNA
• G2 phase


  Proteins needed for Mitosis are produced
• Mitosis


  The process by which the cell nucleus divides into two identical cell nuclei
• In some Human cells interphases lasts 15.3 hours, while mitosis lasts only .7 hours
• Mitosis

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  5. Cytokinesis
• Chromosomes


  • Must duplicate and separate during Mitosis
  • Structures of the tightly packaged DNA
  • DNA is tangled up into a substance of chromatin
  • The chromatin is packaged on the chromosome
• Prophase

  1. Chromosomes now called chromatids because they doubled to form short thick rods which pair up and line up in the center of the nucleus

  2. A centromere connects the two halves of the doubled chromatids

  3. Spindle fibers begin to form

  4. Spindle fiber - a fibrous structure from the cytoplasm which forms to the centriole

  5. Centrioles move to opposite sides of the cell

  6. The nuclear membrane breaks down
• Metaphase

  1. Centromeres of the chromatid pairs line up in the middle of the cell

  2. Metaphase plate- location where the centromeres line up in the center of the cell

  3. By the end of metaphase each chromatid has attached to spindle fibers
• Anaphase


  1. The spindle fibers pull the chromatids apart

  2. This separates each one from its duplicate

  3. These move to opposite sides of the cell

  4. Now there are two identical sets of chromosomes
• Telophase


  1. When the chromosomes reach opposite sides of the cell the spindle fibers break up

  2. The nuclear membrane begins to reform

  3. A furrow begins to develop between the two sets of chromosomes
• Cytokinesis


  The two identical cells completely divide and the cell membrane is completely formed
• Meiosis

  • Diploid (2n) - A cell with two of each kind of chromosome
  • One chromosome from each parent
  • If two body cells were to combine nuclei, the number of chromosomes would double
  • In order for sexual reproduction to occur, each cell involved must reduce its chromosome number by half
  • Haploid (n) - A cell with one of each kind of chromosome
• Haploid cells


  • Gametes
  • Sperm
  • Eggs
• Chromosome number in different organisms

  • Human - 46
  • Pea - 14
  • Fruit fly - 8
  • Dog - 78
• Homologous chromosomes

  • Paired chromosomes with genes for the same trait arranged in the same order
  • Homologous chromosomes may have different alleles on them
• Allele


  Gene form for each variation of a trait of an organism
• Meiosis


  • The process of cell division in which gametes are formed and the number of chromosomes is halved
  • So that sexual reproduction and zygote formation can occur
• Zygote


  Fertilized egg which has a diploid number of chromosomes
• Stages of Meiosis

  1. Interphase - Chromosomes replicate

  2. Each chromosome consists of 2 identical sister chromatids

  3. Prophase I - Each Pair of homologous chromosomes come together to form a tetrad

  4. Tetrad - 2 homologous chromosomes come together and the 4 chromatids overlap

  5. Crossing over - The exchange of genetic material by non-sister chromatids during late prophase I of meiosis

  6. Metaphase I - Homologous chromosomes line up together in pairs

  7. Anaphase I - Spindle fibers attach to the centromeres of each pair

  8. Homologous chromosomes separate and move to opposite ends of the cell

  9. Centromeres DO NOT split like they do in mitosis

  10. Telophase I - Spindle fibers break down

  11. Chromosomes uncoil

  12. Cytoplasm divides

  13. Another cell division is needed because the number of chromosomes has not been reduced

  14. Meiosis II - Is basically just like mitosis, but remember the chromosomes did not duplicate in interphase II

  15. Prophase II - Chromosomes begin to line up in the middle of the cell

  16. Spindle fibers begin to form

  17. Metaphase II - Chromosomes line up on the metaphase plate

  18. Anaphase II - Centromeres split

  19. Sister chromatids separate and move to opposite sides of the cell

  20. Telophase II - Nuclei reform

  21. Spindle fibers disappear

  22. Cytoplasm divides into two

  23. The number of chromosomes in each daughter cell has now been reduced by half
• Meiosis


  The type of cell division that produces gametes
• Gametes


  Sex cells such as sperm cells in males and egg cells in females
• Meiosis

  1. Meiosis 1

  2. Meiosis 2
• Meiosis 1

  1. Prophase 1

  2. Metaphase 1

  3. Anaphase 1

  4. Telophase 1
• Meiosis 2

  1. Prophase 2

  2. Metaphase 2

  3. Anaphase 2

  4. Telophase 2
• Prophase 1


  • Diploid cell
  • Chromatin contains two uncoiled spread out sets of chromosomes
  • DNA replicates
  • Chromosomes condense into X-shaped
  • Homologous chromosomes pair up and bind forming a tetrad
  • Crossing over happens between chromatids of homologous chromosomes
• Metaphase 1


  • Homologous chromosomes line up at the equator and attach to spindle fibers from opposite poles
• Anaphase 1


  • Spindle fibers separate the homologous chromosomes in each tetrad and pull them to opposite poles
• Telophase 1


  • One chromosome from each homologous pair at separate poles
  • Each chromosome still consists of sister chromatids
  • Spindle fibers disappear
  • Nuclear membrane reforms
  • Cytokinesis occurs
• Meiosis 1 outcome

  • Two genetically different haploid daughter cells
  • Each haploid cell contains one set of chromosomes consisting of paired sister chromatids
• Prophase 2


  • Nuclear membrane disappears
  • Spindle fibers fan out from two sets of paired centrioles
• Metaphase 2


  • Chromosomes in each cell line up at the equator and attach to spindle fibers from both poles
• Anaphase 2


  • Sister chromatids of each chromosome separate and move to opposite poles
• Telophase 2


  • Spindle fibers disappear
  • Nuclear membranes reform
  • Cytokinesis occurs
• Meiosis 2 outcome


  • Four genetically different haploid daughter cells
  • Each containing one set of chromosomes
• Meiosis begins with a diploid cell
• Meiosis only produces gametes