1. Chromosomes

2. By the end of this class you should understand: The structure and function of human chromosomes The purpose of the different types of cell division The pattern of chromosome movements in mitosis and meiosis

3. Chromosomes Remember that chromosomes are the packages that our DNA is organized into Normally spread out  Only condensed during cell division

4. Chromatin & Centromere Chromosomes are made of a material called chromatin  A mixture of DNA and protective protein The core in the center is referred to as the centromere  Not always in the center! Sometimes off to one side  Divides the chromosome into two arms which may be uneven (long arm and short arm)

5. Why the X? Remember chromosomes are only compacted during mitosis  Mitosis doubles the chromosome from a I to an X  A visual image of the chromosome is only possible at this stage  This visual stain is called a karyotype

6. Blood Karyotype

7. Actual Karyotype Result

8. Chromosomal duplication Chromosomes are typically spread out in a huge mass of active DNA Only when the cell is about to divide are they packaged tightly  Imagine those blueprints in a busy library, then imagine them packed into books before being shipped away

9. Telomere The tips of chromosomes have long repeated sequences of DNA that are noncoding but protect the rest of the DNA  DNA replication typically fails to completely duplicate these telomeres They function as the aglets on your shoelaces

10. Telomere Shortening Every time a cell undergoes mitosis it loses a bit of its telomeres Adult cells have shorter telomeres and telomere shortening may be linked to aging  Dolly the sheep was cloned from an adult cell and so may have showed premature aging

11. Telomerase Immortal cells such as stem cells and cancer cells express an enzyme called telomerase  Lengthens telomeres and extends life of daughter cells Research in stem cells and telomerase may provide clues into aging process

13. Cell Replication One cell can become two identical cells through a process called mitosis One cell can also become four haploid cells through a process called meiosis  These are the only two ways to make more cells in your body  Picture: cytoskeletal stain of cell in mitosis

14. Mitosis & Meiosis MITOSIS: Produces two cells identical to original Many stem cells in your body constantly perform mitosis to grow new tissue This is how you grow MEIOSIS: Produces four haploid cells Only certain stem cells in the gonads perform meiosis This is how you make sex cells (gametes)

15. Mitosis & Cell Cycle Mitosis is actually only a part of the cell replication cycle Cells that are amitotic (such as brain cells) are in G0 phase and never self- replicate

16. Interphase Actually several major stages of cell growth G1: “Okay, guess I'll get ready to divide” S: “Gonna need to copy my DNA” G2: “And I'll need spindle fibers to do the job”

17. Phases of the Cell Cycle

18. Phase control Each phase of the cell cycle has controls  The cell can only move to the next phase when given “permission”  What is the name for when these controls break?

19. Steps of Mitosis A video is worth a thousand words! http://www.youtube.com/watch?v=VlN7K1- 9QB0 Key detail: the microtubule spindles that pull the chromosomes apart come from the centromere and are a type of cytoskeleton structure

20. Mitosis Diagram part 1

21. Mitosis Diagram part 2

22. Mitosis Summary!

23. Meiosis Meiosis is a specialized type of cell replication It produces gametes (sex cells)  Sperm and eggs in humans and animals  Pollen and seeds in plants  Bacteria cannot undergo meiosis

24. Steps of Meiosis Meiosis is similar to a double mitosis  Chromosomes are duplicated  46 x 2 = 92 chromosomes At the end there are four cells with only one set of chromosomes  23 chromosomes x 4 gametes

25. Double Mitosis?? Yes! They even have the same steps:  Prophase I, Metaphase I, Anaphase I, Telophase I  Prophase II, Metaphase II, Anaphase II, Telophase II In Meiosis I, the homologues are separated In Meiosis II, the sister chromatids are pulled apart as in Mitosis

26. Meiosis I

27. Meiosis II

28. To Summarize:

29. See you in lab!