Mitosis, Meiosis & Cancer Academic Biology

1. Mitosis, Meiosis & Cancer Academic Biology

2. Types of Cells A. Somatic (Body Cells) - Have 46 Chromosomes B. Gametes (Sex Cells) - Egg & Sperm - Have 23 Chromosomes

3. Cell Growth & Limiting Factors A. Cell size can vary greatly. i.e. Red Blood cells (8um) & Nerve cells (1m) B. Cell size is limited. “Bigger is not Better!” • Diffusion - Decreases as a cell grows. - Will take longer for waste to exit a cell or building blocks to enter a cell. - Protein production is decreased. (DNA overload)

4. III. Chromatin versus Chromosomes A. Chromatin - DNA when a cell is not dividing. - Loosely packed DNA that is wrapped around proteins (Histones).

5. B. Chromosomes - DNA when a cell is dividing! - Composed of tightly bound chromatin. Steps 1-3: DNA forms a chromosome, also called a chromatid. Step 4: The chromosome has replicated. Step 5: Duplicated chromosome, before division.

6. IV. Why do cells divide? A. To replace old, worn out cells. B. To replace injured / damaged cells. C. For an organism to grow. D. For reproduction to occur.

7. V. The Cell Cycle A. Growth & division of “somatic” cells. B. A cell has 2 general periods: 1. Interphase – The growth period. 2. Division – The production of 2 “daughter” cells.

8. C. Stages of the Cell Cycle: 1. INTERPHASE (3 sub-phases) a. G1 - Period of rapid cell growth. - Synthesize new organelles - Lasts roughly 11 hours. b. S - Will begin if the “Restriction Point” is passed. - DNA is synthesized / Chromosomes are copied. - Lasts roughly 7 hours. c. G2 - All organelles are copied - Lasts roughly 3 hours.

10. D. TERMS: Chromatid & Sister Chromatids a. Chromatid - One identical copy of a chromosome. b. Sister Chromatids - Two identical chromatids connected together by the centromere. - Spindle fibers from centrioles will connect to the kinetechore (portion of centromere).

11. 2. MITOSIS (P.M.A.T) STEPS: 1. Prophase - DNA coils & becomes chromosomes - The chromosomes have already duplicated themselves and have 2 identical halves called “Sister Chromatids.” - The nuclear envelope disappears.

12. 2. Metaphase - The chromosomes (Sister Chromatids) line up along the equator. 3. Anaphase - All sister chromatids are pulled apart by spindle fibers from the centrioles. - One chromatid moves to each side of the cell. - Remember, each cell only gets 46.

13. 4a. Telophase - The nucleus reappears. - Chromosomes uncoil into chromatin. 4b. Cytokinesis - The cytoplasm finally breaks in two. End Result: Two new identical cells.

17. Chromosome Numbers A. Diploid - Refers to cells which carry a double set of chromosomes. B. Haploid - Refers to cells with just one set of chromosomes. C. Homologous Chromosomes - Refers to two chromosomes which are similar in structure. - Each contains the same genes.

18. MEIOSIS • What is it? - The formation of gametes. - Produces 4 cells, each with half the original chromosome number. Comparison to Mitosis: - 2 Cell Divisions (8 Phases). - 4 Cells with 23 chromosomes. - Cells are not identical.

19. II. Meiosis I (1st Division) A. Prophase I - Synapsis occurs: * Process of homologous chromosomes finding each other. - Tetrads form: * Two pairs of homologous sister chromatids combined together.

20. - Crossing-Over occurs. * Process where two homologous chromosomes “exchange” genetic information. - Each chromatid is now different. - Leads to variation & evolutionary change. (Click image for animation.)

21. B. Metaphase I - 23 Tetrads line up along equator. C. Anaphase I - Tetrads are separated. - Homologous chromosome pairs moves in opposite directions. D. Telophase I - 2 new cells are formed. - Each cell has 46 chromosomes, or 23 sister chromatids. - SO…….23 X’s

23. III. Meiosis II (2nd Division) A. Prophase II - Nothing different. B. Metaphase II - Chromosomes line-up along equator. - 23 X’s. C. Anaphase II - Centromeres break down and sister chromatids split.

24. D. Telophase II - 4 cells produced each with 23 chromosomes. - Each cell is considered Haploid (n). = 23 Chromosomes. - Original cell was Diploid (2n). = 46 Chromosomes.

27. Possible Errors A. Mutations - An error or change in the DNA sequence. 1. Non-Disjunction - Failure of chromosomes to separate properly during meiosis. - Results in an extra or missing chromosome(s). Examples: Trisomy 21 and Turners Syndrome

28. B. Karyotype A picture of chromosomes taken during prophase of cell division. 1. Can be used to diagnose chromosomal disorders /abnormalities. 2. 46 chromosomes break down into 23 pairs. a. 22 pairs are referred to as autosomes.

29. b. There is one pair known as the sex chromosomes. 1. Males have an X and a Y. 2. Females have 2 X’s.

30. Karyptype Ex. • Turners Syndrome

31. Karyotype Example • Downs Syndrome

32. Karyotype Example • Edward’s Syndrome

33. Syndromes: • A few syndromes that can be detected using a karyotype are: • Down’s Syndrome- Usually occurs when a person has an extra chromosome # 21 • Klinefelter’s Syndrome- Occurs when a person has 2 X chromosomes AND a Y • Turner’s Syndrome- Occurs when a person has only one X chromosome and no Y • Fragile X – Occurs when the X chromosome appears to have a break or tear. • Edwards Syndrome – Occurs when an individual has an extra #18 chromosome. • Cri Du Chat – Syndrome classified by missing all or part of chromosome #5.