1. Cellular Reproduction Beginning with Chromosomes

2. Duplicated chromosomes (sister chromatids) TEM Tight helical fiber Looped domains TEM Centromere Nucleosome “Beads on a string” Histones DNA double helix Figure 8.4 DNA double helix Chromatin

3. DNA DNA is found in chromosomes Chromatin consists of DNA and proteins called histones and surround the DNA in a spiral shape Organisms can reproduce sexually or asexually. Amoeba reproduce asexually

4. Vocabulary Check 1. What is a histone? 2. What is a nucleosome? 3. What is chromatin? 4. What is a centromere?

5. CELL DIVISION MITOSIS & MEIOSIS Mitosis = somatic cell division http://youtu.be/1cVZBV9tD-A Meiosis = egg and sperm division http://youtu.be/rB_8dTuh73c http://youtu.be/1cVZBV9tD-A http://youtu.be/rB_8dTuh73c CELL DIVISION MITOSIS & MEIOSIS Mitosis = somatic cell division http://youtu.be/1cVZBV9tD-A Meiosis = egg and sperm division http://youtu.be/rB_8dTuh73c http://youtu.be/1cVZBV9tD-A http://youtu.be/rB_8dTuh73c

6. Interphase Mitotic Cell Cycle 2 distinct phases What's the most important event of interphase? Chromosome duplication S G2G2 G1 G0 Non reproducing cells

7. Cell Cycle results in the production of two cells, each with the same amount of genetic material and the same genetic information

8. All chromosomes are duplicated Do they contain identical genes? What is significant about DNA in the S and G 2 phases? That means: two copies of each chromosome What are the copies called? Sister chromatids Yes, but… What about meiosis?

9. Some terminology Double-chromatid chromosomes Single-chromatid chromosomes Chromatin Homologous chromosomes Chromatid When do each of these occur?

10. MITOSIS

11. Interphase – this is when DNA is duplicated (actually, this is not part of mitosis itself) Prophase Metaphase Anaphase Telophase Interphase – this is when DNA is duplicated (actually, this is not part of mitosis itself) Prophase Metaphase Anaphase Telophase THE STEPS OF MITOSIS

12. Stages of Mitosis – G2, prophase, metaphase, anaphase, telophase and cytokensis (cytokenesis occurs during telophase)

13. Onion root tip Whitefish blastula Interphase Nuclear envelop intact Chromosomes duplicated but not apparent 2 nucleoli visible in onion root tip Nucleoli not visible in whitefish blastula Mitosis DNA loose, uncondensed, called chromatin

14. Onion root tip Whitefish blastula Prophase Mitosis Double-chromatid chromosomes evident Chromatin becomes super-coiled & compact Nuclear envelop breaks down Nucleoli disappear in onion root tip Centrioles migrate toward poles of cell forming the spindle. Mitotic spindle begins to form

15. Double-chromatid chromosomes

16. Onion root tip Whitefish blastula Metaphase Mitosis Double-chromatid chromosomes line up on equatorial plate of cell The spindle fibers attach to the chromosomes at the centromeres

17. Onion root tip Whitefish blastula Anaphase Mitosis Centromeres are pulled apart Groups of single-chromatid chromosomes move opposite poles of the cell Spindle fibers pull chromatids apart

18. Onion root tip Whitefish blastula Telophase Mitosis Cytokinesis begins with appearance of cleavage furrow Cytokinesis begins with appearance of cell plate Groups of single-chromatid chromosomes reach poles of cell Nuclear envelop begins to reform Nucleoli reform 2 new daughter cells formed

19. Onion root tip Whitefish blastula Returning to Interphase Mitosis Cytokinesis completes Chromosomes ‘disappear’ as interphase chromatin reforms 2 new daughter cells enter G 1 phase of the cell cycle

20. A SUMMARY OF MITOSIS

21. Mitosis Questions 1.What does “diploid” mean? 2.We have __ total chromosomes. 3.In the term 2n, what does “n” stand for in us? In a gypsy moth? 4.Why does mitosis occur? Major functions? 5.In what cells (general term) does mitosis occur? 1.What does “diploid” mean? 2.We have __ total chromosomes. 3.In the term 2n, what does “n” stand for in us? In a gypsy moth? 4.Why does mitosis occur? Major functions? 5.In what cells (general term) does mitosis occur?

22. Mitosis Questions 6. What are chromatids? 7. What happens in Anaphase to result in each new cell receiving duplicate parental DNA? 8. In a species whose diploid number is 224, what would its sperm/eggs contain? 6. What are chromatids? 7. What happens in Anaphase to result in each new cell receiving duplicate parental DNA? 8. In a species whose diploid number is 224, what would its sperm/eggs contain?

23. Why is this duplication of parental DNA necessary? Something to do with passing on genetic information?

24. Why undergo mitosis at all? Something to do with cells getting damaged, old, lost? Something to do with the organism growing, infant to adult?

25. SOMATIC CELLS What is the process of somatic cell duplication called? What are typical body cells called? These cells divide continuously The new cells receive an exact copy of all the parent cell’s: Mitosis DNA

26. What are these somatic cells? Diploid or 2n What does this mean? They contain the full number of chromosomes in pairs How many in humans? 46 23 pairs Know this!

27. Mitosis occurs only in somatic cells Gametes are not diploid (2n) Instead, they are haploid (n) Gametes are not diploid (2n) Instead, they are haploid (n) What about sex cells? Called gametes Eggs and sperm Produced in ovaries or testes

28. Our haploid (n) number is 23 So our eggs and sperm have how many chromosomes? Half the number Why?

29. Homologous chromosomes Carry the same genes

30. MEIOSIS Mitoses results in identical cells and is used for replacement of dead or worn out cells, wound repair and growth Meiosis is strictly to produce eggs or sperm cells which are diverse from the parent cell and are used in sexual reproduction

31. Fertilization is the union of an egg and a sperm If the egg and sperm were both diploid, what would the fertilized egg (zygote) be?

32. It would be a genetic mess! At fertilization, n + n = 23; 23 + 23 = 46! Instead, gametes are haploid (n). Egg and sperm both have exactly half the number of chromosomes of somatic cells

33. Note how mitosis and meiosis differ: Number of divisions? Number of chromosomes? Number of products? Number of divisions? Number of chromosomes? Number of products?

34. Meiosis ! Meiosis is the cell division process that enables the transformation from 2n to n Somehow somatic cells (2n) in our ovaries or testes must produce gametes (n)

35. Multicellular diploid adults (2n  46) MEIOSIS FERTILIZATION MITOSIS 2n2n and development Key Sperm cell n n Diploid zygote (2n  46) Diploid (2n) Haploid (n) Egg cell Haploid gametes (n  23) Figure 8.12

36. How is meiosis more complicated than mitosis? Each chromosome has a partner Gametes must contain precisely half the diploid number of chromosomes They must contain one of each homologous pair of chromosomes Remember karyotypes? They come in pairs One from mom One from dad

37. Human Karyotype

38. Which pair of chromosomes in us in not homologous? All our other pairs of chromosomes are homologous and are called autosomes It’s the 23rd pair in males, the XY pair Remember what homologous means?

39. What are the divisions called? How many divisions does meiosis have?

40. Duplicated chromosome (two sister chromatids) MITOSIS Prophase Chromosome duplication Chromosomes align at the middle of the cell. Metaphase Sister chromatids separate during anaphase. Anaphase Telophase Daughter cells of mitosis 2n2n 2n2n Prophase I Metaphase I Anaphase I Telophase I MEIOSIS Chromosome duplication Homologous chromosomes come together in pairs. MEIOSIS I Site of crossing over between homologous (nonsister) chromatids Homologous pairs align at the middle of the cell. Chromosome with two sister chromatids Homologous chromosomes separate during anaphase I; sister chromatids remain together. Daughter cells of meiosis I Sister chromatids separate during anaphase II. Haploid n  2 MEIOSIS II Parent cell (before chromosome duplication) 2n  4 Daughter cells of meiosis II n n n n Figure 8.15

41. Prophase I has four times as much genetic material Crossing over occurs in prophase I but NOT in prophase II

42. 1234 1.One pair of homologues to start 2.DNA is replicated 3.Meiosis 1 = 2n ---> n 4.Meiosis 2 = chromatids separate into 4 products

44. In males, how many progeny are produced? Typically 4 viable sperm are produced following each Meiosis 2

45. In females, how many progeny are produced? Just one viable ovum (egg) is produced, plus 3 small polar bodies

46. Side by Side Comparision of mitosis and meiosis http://www.pbs.org/wgbh/nova/baby/divi_flash.html

47. Genetic Variation

48. Independent Assortment

49. Crossing over When does it occur? Only during Prophase of Meiosis 1 Homologous chromosomes get together in temporary tetrads Overlap (cross over) and trade their DNA Why is this a good thing to do, generally?

50. Meiosis Summary 1.Meiosis 1 a.DNA replication takes place b.A parent cell produces two daughter cells each with one member of each original pair of homologous chromosomes (to create haploid daughter cells) c.Crossing over may occur 1.Meiosis 1 a.DNA replication takes place b.A parent cell produces two daughter cells each with one member of each original pair of homologous chromosomes (to create haploid daughter cells) c.Crossing over may occur

51. Meiosis Summary 2.Meiosis 2 a.There is no more DNA replication b.The chromatids of each chromosome separate and each daughter cell divides c.At the end of Meiosis 2, there are 4 daughter cells from each parent cell. Each daughter cell has half the number of chromosomes as the parent cell 2.Meiosis 2 a.There is no more DNA replication b.The chromatids of each chromosome separate and each daughter cell divides c.At the end of Meiosis 2, there are 4 daughter cells from each parent cell. Each daughter cell has half the number of chromosomes as the parent cell

52. 1.The cells produced in meiosis are _____ (haploid or diploid?) 2.Sex cells are called ________. _____ are produced by males, ____ by females. 3.What’s crossing over and why is it important? 1.The cells produced in meiosis are _____ (haploid or diploid?) 2.Sex cells are called ________. _____ are produced by males, ____ by females. 3.What’s crossing over and why is it important? Meiosis Questions

53. 4. In what meiotic stage does crossing over occur? 5. Why are sex cells n, not 2n? 6. If a species’ diploid number is 50, what is n? 4. In what meiotic stage does crossing over occur? 5. Why are sex cells n, not 2n? 6. If a species’ diploid number is 50, what is n? Meiosis Questions

54. Cancer Cells: Growing Out of Control –Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle. –Cancer is a disease of the cell cycle. –Cancer cells do not respond normally to the cell cycle control system.

55. When Meiosis doesn’t work Nondisjunction Down Syndrome an extra chromosome 21 Trisomy 21 and Down Syndrome XXY – Klinefelter syndrome (males) XYY – looks normal (male) XXX – (female) Looks normal XO – Turner syndrome (female)

56. Meiosis I Abnormal gametes Gametes Nondisjunction: Pair of homologous chromosomes fails to separate. NONDISJUNCTION IN MEIOSIS I Number of chromosomes Meiosis II Nondisjunction: Pair of sister chromatids fails to separate. Abnormal gametes Normal gametes n n n  1 n – 1 n  1 NONDISJUNCTION IN MEIOSIS II n – 1 Figure 8.20-3

57. Resources http://www.pbslearningmedia.org/asset/lsps07_int_celldivision/ http://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/cellcycle- mitosis-meiosishttp://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/cellcycle- mitosis-meiosis Essentials of the Living World – Textbook Education-Portal Short videos covering all aspects of cell divisionEducation-Portal Mitosis Quiz See how you do on this quiz!Mitosis Quiz Mitosis Exam OK, here are 20 more questions!Mitosis Exam Meiosis Quiz Meiosis Exam

58. Vocabulary DNA Chromosome Chromatin Histone Nucleosome Centromere Sister chromatids Mitosis Meiosis Homologous chromsomes Chromatid Interphase Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis Spindle fiber Diploid Haploid Apoptosis Somatic Sex cell Gametes Zygote Karyotype Tetrad Crossing over Independent assortment Nondisjunction Down syndrome Trisomy Cancer Klinefelter syndrome Turner syndrome