1. Chapter 7: Cell Cycle and Cell Division WASILLA HIGH SCHOOL 2014 - 2015

2. Asexual Reproduction: Binary Fission and Mitosis  Rapid, effective way to make new individuals  Genetic clones  Binary fission – how prokaryotes reproduce by splitting into two new cells  Mitosis – how our somatic (body) cells reproduce

3. Importance of Cell Division  Reproduction  Growth  Repair and regeneration of tissues

4. Eukaryotic Cell Cycle  Interphase  Mitosis (PPMAT)  Prophase  Prometaphase  Metaphase  Anaphase  Telophase  Cytokenisis

5. Interphase  Broken into three major stages:  Gap 1 (G1): Normal cell functions occurs  Synthesis (S): DNA is "synthesized" meaning it is replicated  G2: The cell prepares for mitosis

6. Prophase  Condensed chromosomes appear  Consist of DNA coiled around histone proteins into nucleosomes  Nucleosomes coil up tightly into chromatin  Chromatin supercoils even tighter into chromosomes  The centrosome, which is made up of a pair of centrioles, moves to opposite ends of the nucleus  Spindle fibers begin to extend towards the kinetochores on the chromosomes

7. The next "three" phases of PPMAT Prometaphase Nuclear envelope disappears Microtubles attach to the kinetochores on the chromosomes Metaphase: chromosomes line up at the M iddle Anaphase: chromatids move A part and toward the other poles

8. What makes the chromosomes move?  Kinetochores contain a protein called cytoplasmic dynein  Acts like the rod on a fishing reel and pulls the chromatids toward the centriole poles

9. Telophase and Cytokinesis  Telophase: the nucleus splits in T wo  Nuclear envelope reappears  Chromosomes start to relax  Cytokinesis: the division of cytoplasm  Animal Cells: A cleavage furrow forms and two proteins cause a contraction to occur, pinching one cell into two new daughter cells.  Plant Cells: Plants have cell walls  Vesicles arrive bringing the materials to make a new cell plate  The cell plate is what becomes the new cell wall

10. So what about my gametes?  I'm so glad you asked!  Mitosis creates genetically identical clones in your body cells  Ensures that each cell contains the same instructions  Each cell is considered a Diploid (2N) because it contains two copies of the DNA  "N" means how many copies of DNA there are  Gametes are your sex cells: Sperm and Eggs  Undergo a similar process of splitting called Meiosis

11. How is Meiosis different from Mitosis? Mitosis  Somatic (body) cells  Creates 2 genetically identical daughter cells  Basically makes cloned cells  Only involves one division  Cells are 2N or diploid Meiosis  Gametes (sex cells)  Creates 4 genetically different daughter cells  Each cell is unique and ensures species diversity in your offspring  Involves two divisions  Cells are 1N or haploid

12. Two Divisions? Absolutely!  Meiosis I  Prophase  Metaphase  Anaphase  Telophase  Meiosis II  Prophase  Metaphase  Anaphase  Telophase

13. Meiosis I begins with Homologous Chromosomes  Homologous Chromosomes  Two pairs of the same genes  One comes from Mom another from Dad so they might not be identical but they will still code for the same genes  Prophase I begins with the Homologous chromosomes P airing up and lining up together  Something special happens here called Crossing Over  We will discuss this in more detail in a few slides!  During anaphase I the homologous chromosomes split apart  By the end of Meiosis I you have 2 genetically different Haploid cells

14. Meiosis II  The individual chromosomes undergo a second mitotic division  End result is 4 genetically different haploid cells, each with a single copy of every gene in your body

16. Genetic Diversity and Its Importance  A diploid organism (like you) has two copies of DNA in its somatic body cells  One from mom  One from dad  Genetic shuffling and diversity leads to a hardy species better suited to survival  Think about what happens with inbreeding – more disease, more mutations, more ewwww….  We have an evolutionary drive to keep our genes diverse which is why we think "eww" with inbreeding

17. Two Major Mechanisms Leading to Diversity  Crossing Over – occurs during Prophase I of Meiosis  Homologous chromosomes pair up and exchange pieces of genetic material  Forms tetrads or bivalents  Chiasmata form  Places where genetic material is exchanged between the homologous chromosomes  Crossing over results in genetic recombinants

18. Two Major Mechanisms Leading to Diversity  Independent assortment: One of Gregor Mendel's postulates  Chance decides what homologous pair goes to which daughter cell during anaphase I  The greater the number of chromosomes, the lower the probability of reestablishing the original parental combinations  Your children will be a combination of four people: both you and your mate's parents  Each of your gametes contain chromosomes that are a combination of both your parent's DNA

19. What happens when meiosis doesn't go right?  Nondisjunction – When a homologous chromosome doesn't separate like its supposed to  Trisomy – having an extra chromosome (example is Down's Syndrome – trisomy 21)  Aneuploidy – missing a copy of a chromosome  Polyploidy  Most organisms are haploid (1N) or diploid (2N)  Some can become triploid (3N), tetraploid (4N) or higher (polyploid))  Translocation – crossing over gone bad