DNA Terminology…. The Cell Cycle…. Mitosis and Meiosis…..

1. DNA Terminology…. The Cell Cycle….Mitosis and Meiosis…..

2. I. Chromosomes A. DNA wrapped around proteins (histones) is a nucleosome B. Uncoiled, threadlike DNA is Chromatin (non-dividing cell) C. DNA called a chromosome in dividing cells; short, fat rods

3. Half of a doubled Chromosome = a Chromatid 1.Contains two identical parts 2. Attach at a point called the Centromere E. Homologous Chromosomes • Occurs in pairs; same size and shape • Structurally different from all other pairs 3. Have the same gene locations chromatid centromere

4. F. Gene Eye Color 1. Distinct unit on a chromosomes 2. Sequence of nucleotides

5. II. “N” Number = The number of chromosomes a cell has • Diploid (2N) • Each species has a characteristic number of chromosomes • Cells with both chromosomes of every pair called somatic or body cells • 2N for humans = 46 • Ex: Crayfish (200) fruit flies (4)

6. Haploid (1N) • Cell with 1 chromosome of each pair • Sex cell (sperm or egg)-Gametes

7. III. Asexual and Sexual Reproduction A. Mitosis is Asexual • Functions include • Unicellular Organism = Reproduction b) Multi-cellular Organisms • Growth and development from egg • Replacement of dead or damaged cells c) Passes along the genome (total DNA per species) • Each daughter cell is clone of parent.

8. B.Meiosis is Sexual • Mixes DNA • Produces ½ the number of the chromosomes of the parents • Cells involved in sexual reproduction are sperm and eggs (gametes)

10. IV. Cell Division • Prokaryotes: Called Binary Fission • Eukaryotes: Use the Cell Cycle • Interphase • Mitosis • Cytokinesis

11. V. Cell Cycle • = sequence of growth and division in the life of a cell

12. G1 (growth;Gap 1) 11 hrs. • Rapid cell growth • Cell doubles in size • Enzymes + organelles double in number S=Synthesis • Growth • DNA makes a copy of itself Cytokinesis 1 hr. Interphase Mitosis G2=Gap 2 7 hrs. • Rapid Growth • Final preparation for cell division 3 hrs.

13. Cell Cycle = Interphase = period of cell growth and duplication of the DNA G1 + S + G2 Mitosis = division of the cell’s nucleus in which the chromosomes in the parent cell divides into 2 identical sets Cytokinesis = cytoplasm divides in 2 daughter cells

16. VI. Stages of Mitosis Prophase a) Early Prophase • Chromatin coils to chromosomes • Nucleolus & nuclear membrane break down & disappear • Centrioles move to poles (animal cells only).

17. Middle Prophase • Spindle fibers (microtubules) appear • Polar – centriole to centriole • Kinetochore – centromere to centriole

18. Late Prophase • Aster appear (centriole and fibers) 2) Chromosomes position is random

19. Metaphase • Kinetochore fibers move chromosomes • Chromosomes line up along equator

20. Anaphase • Centromere splits • Sister chromatids pulled to opposite ends

21. Telophase • Identical chromatids at opposite end • Chromatids unwind & elongate to chromatin • Centrioles & spindle disappear • Nucleolus & nuclear membrane reappear

22. 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

23. Cytokinesis • Animal cells form cleavage furrows • Plant cells form a cell plate

26. VII. Reproduction and Meiosis • Meiosis in males ♂ 1. Part of spermatogenesis 2. Occurs in the testes 3. Always results in four sperm cells

27. Meiosis in females ♀ • Part of oogenesis • Occurs in the ovaries • One cell receives most of the cytoplasm; the other 3 cells are polar bodies • Results in mature egg ( with 23 chromosomes)

28. VIII. Significance of Meiosis • Produces genetic variation • Without meiosis, chromosome numbers would continually increase (teenage mutant Ninja turtles)

29. IX. Review “N” Number Mitosis => results in 2N Meiosis => results in 1N animals (1N) plants (1N) egg and sperm spores and seeds (gametes) fuse (2N zygote) *♂ - sperm all viable after spermatogenesis *♀ - after oogenesis, 1 egg(ootid) and 3 polar bodies (no cytoplasm, just DNA)

31. X. Steps of Meiosis (2 Separate Divisions)

32. Meiosis vs Mitosis

33. Meiosis I (starts with 2N) Prophase I • Chromatin shortens and coils to chromosomes • Spindle appears • Nucleolus and nuclear membrane disappear • Unique step: • Chromosomes line up next to their homologs (called synapsis) • Homolog pairs twist tightly to form a tetrad • (4 chromatids that make up two doubled chromosomes) • Crossing over can occur; exchange of DNA between homologs and/or 2 sister chromatids

34. Tetrad Formation

38. Tetrad Formation

40. Meiosis I Metaphase I • Tetrads move to the equator; homolog pairs stay together Anaphase I • Homologous pairs separate and move to each pole ( one chromosome of each pair pulled to pole) • 2 chromatids still joined at centromere

41. Meiosis I Telophase I • Cytoplasm divides forming 2 daughter cells

43. Meiosis II (chromosomes do not double; ends with 4 (1n) cells Prophase II • New spindle forms • Nuclear membrane and nucleolus break apart • Chromatin shortens and becomes visible as sister chromatids Metaphase II • Sister chromatids move to the equator

45. Meiosis II Anapahse II • Centromere divides; sister chromatids move to opposite poles Telophase II • Nuclear membrane reforms; Spindle disappears • Cytokinesis occurs • 4 daughter cells from one parent