Chapter 8
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Chapter 8






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    Chapter 8 Chapter 8 Presentation Transcript

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