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Chapter 8


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Chapter 8

  1. 1. Chapter 8 Cell Reproductin Mitosis and Meiosis
  2. 2. What’s a Chromosome?
  3. 4. Parts of Chromosome <ul><li>A chromatid is a ½ of the chromosome or one arm. </li></ul><ul><li>A centromere is the place where the two halves of the chromosome are held together. </li></ul><ul><li>The centromere is at different locations depending on the chromosome type. </li></ul>
  4. 5. Types of Chromosomes <ul><li>Sex chromosomes determine the gender of the organism and also carry genes for other characteristics. They are the last or 23 rd pair. </li></ul><ul><li>Males are XY and females are XX. </li></ul><ul><li>Autosomes are body chromosomes not involved with sex. </li></ul><ul><li>Autosomes carry the rest of the traits for an organism. </li></ul><ul><li>Every organism that reproduces sexually carries two of every chromosome. The two copies are called homologous chromosomes. </li></ul>
  5. 7. Types of Cells <ul><li>A diploid cell have both sets of homologous chromosomes. </li></ul><ul><li>All normal cells except reproductive cells are diploid. </li></ul><ul><li>A haploid cell have ½ the normal number of chromosomes. </li></ul><ul><li>All sex cells such as egg and sperm are haploid because they need to join during fertilization to produce a new organism. </li></ul>
  6. 9. Cell Division <ul><li>Mitosis is when one cell divides into two diploid, identical daughter cells. </li></ul><ul><li>Mitosis occurs to reproduce all types of cells except sex cells. </li></ul><ul><li>Meiosis is when one cell will divide and create 4 haploid daughters cell that are different from each other. </li></ul><ul><li>Meiosis occurs in sex cells only. </li></ul>
  7. 10. The Cell Cycle <ul><li>The cell cycle is a repeated set of events that make up the life of a cell. </li></ul><ul><li>The time between cell divisions is called interphase. </li></ul><ul><li>Interphase is the longest part of cell life. </li></ul><ul><li>After interphase comes M phase and then cytokinesis. </li></ul>
  8. 11. Interphase <ul><li>The first stage of interphase is called G 1 phase. Cells grow to mature size. </li></ul><ul><li>The second stage is called S phase. The cell’s DNA is copied. </li></ul><ul><li>The last stage is called G 2 phase. The cell prepares to divide and grows a little more. </li></ul><ul><li>Sometimes a cell will exit the cycle. This is called G 0 . Some cells like nerve cells stop dividing permanently once they reach maturity. </li></ul>
  9. 13. Mitosis <ul><li>Mitosis consists of 4 phases. </li></ul><ul><li>Prophase, metaphase, anaphase and telophase/cytokinesis. </li></ul><ul><li>Mitosis happens in diploid cells only. </li></ul><ul><li>2 identical daughter cells are formed. </li></ul><ul><li>Cancer results when mitosis runs out of control. </li></ul>
  10. 14. Prophase <ul><li>1. DNA turns into chromsomes. </li></ul><ul><li>2. Centrosomes appear next to the disappearing nucleus. </li></ul><ul><li>3. Each centrosome contains a pair of centrioles. </li></ul><ul><li>4. Spindle fibers appear that radiate from the centrosomes. </li></ul>
  11. 15. Metaphase <ul><li>1. The spindle fibers attach to the centromere of each chromosome. </li></ul><ul><li>2. The chromosomes line up along the center of the cell. </li></ul>
  12. 16. Anaphase <ul><li>1. The chromatids of each chromosome separate at the centromere. </li></ul><ul><li>2. The chromosomes move to opposite ends of the cell being pulled by the spindle fibers. </li></ul>
  13. 17. Telophase/Cytokinesis <ul><li>1. The spindle fibers begin to disapper. </li></ul><ul><li>2. The chromosomes begin to coil again become invisible. </li></ul><ul><li>3. The nucleus reforms in each cell. </li></ul><ul><li>4. A cleavage furrow forms separating the two new cells. </li></ul><ul><li>*A cell plate forms in plant cells. </li></ul>
  14. 21. Meiosis <ul><li>Only occurs in sex cells, sperm and egg. </li></ul><ul><li>Creates 4 haploid cells that are different from each other. </li></ul><ul><li>That is the reason why siblings don’t look exactly alike but may be similar. </li></ul><ul><li>Meiosis is divided into Meiosis I and Meiosis II. </li></ul>
  15. 25. Important Events <ul><li>During Prophase I, crossing over occurs. </li></ul><ul><li>Crossing over creates genetic recombinations that result in different cells. </li></ul><ul><li>This assures that the genes from mom and dad are mixed. </li></ul><ul><li>Homologous chromosomes cross over and form a tetrad when they do this. </li></ul>
  16. 26. Crossover
  17. 28. Reproduction <ul><li>Asexual reproduction occurs with only 1 parent. </li></ul><ul><li>No gametes are produced in asexual reproduction and the offspring is a genetic clone of the parent. </li></ul><ul><li>Sexual reproduction uses meiosis to create gametes (sperm and egg). </li></ul><ul><li>The offspring are genetically different from each other and the parent. </li></ul><ul><li>Some organisms can reproduce both ways. </li></ul><ul><li>In hard times, some plants reproduce asexually while in times of plenty, they can reproduce sexually. Some animals can also do this. </li></ul>