Chromosomes and Mitosis

1. Chromosomes and Mitosis Lecture 6

2. 1 Chromosomal Basis of Heredity • A gene is a unit of heredity • Genes are carried on DNA • DNA is contained within chromosomes as chromatin

3. Chromosomes replicate during cell division

4. The chromosome complement

5. Chromosome analysis Cri Du Chat results from loss of a small piece of chromosome 5

6. Gene Map

7. Chromosome pairs

8. Non-identical genes

9. Sex chromosomes • These determine the sex of an individual • Two X chromosomes make a female • One X and one Y a male

10. Two types of Cell Division • Cells divide for two reasons • To create genetically identical copies of themselves • This is mitosis • To create gametes that contain half of the chromosomes of the original cell • This is meiosis 46 46 23 23 23 23 46 46

11. The Cell Cycle

12. S phase Condensation Replication Schematic

13. DNA replication Duplex DNA begins Replicating Replication bubbles merge creating two duplexes

14. Mitosis

15. The stages of Mitosis

16. Prophase Detail

17. Prometaphase

18. Metaphase

19. Anaphase

20. Telophase

21. The sum total of the process

22. Karyotypes

23. Chromosome Length

24. Chromosome appearance

25. Meiosis and Gametogenesis

26. Somatic and Germline cells • Development of a fertilized egg into an adult results in two distinct types of cells • Somatic cells • These create all tissues and organs of the adult except for cells destined to become sperm or egg • They can only undergo mitosis • Germline cells • The final differentiated form of these cells are mature gametes: the sperm and egg • These cells undergo mitosis until gametogenesis • They then undergo meiosis

27. Meiosis

28. Meiosis is required for gametogenesis

29. Meiosis I Somatic cells Germline Cells

30. Interphase I and Prophase ILeptotene

31. Prophase IZygotene

32. Prophase IPachytene

33. Prophase IDiplotene

34. Recombination

35. And on the molecular level

36. Metaphase I and anaphase I

37. Meiosis I is the reduction division

38. Non-disjunction

39. Telophase I

40. Cytokinesis sperm formation oocyte formation

41. Meiosis II

42. A comparison of meiosis and mitosis

43. Relationship to Gametogenesis

44. Sperm and Egg formation

45. Gametogenesis

46. Fertilization • Entry of a single sperm into an egg prevents entry of other sperm • The DNA of sperm and egg are initially kept separate in “pronuclei” of the zygote • Timing of a pregnancy extends from the “last menstrual period” (LMP) rather than the time of fertilization

47. Mitotic Non-disjunction

48. Cell cycle and apoptosis • Cells undergo 3 controlled processes • The first two are part of the cell cycle, the last an exit from the cell cycle • Division (the cell cycle) • Quiescence • This is where most of the work of being a cell lies • During division the energy of the cell is devoted to making a new cell • Death • This can be a normal process creating a final functional form or an induced suicide • Epithelium and reticuloendothelial cells undergo active transitions towards terminally differentiated states in which the final forms are unable to divide • The stratum corneum consists of cells that have become bags of crosslinked keratin protein with no internal metabolism • Suicide can be induced because the organism senses a threat to the entire organism • Infection, cancer, avoidance of autoimmunity

49. Control of entry into cell cycle and apoptosis • Cell cycle is initiated by phosphorylation of transcription factors • These activate transcription of a set of proteins known as cyclins • The appearance of cyclins is progressive and determines the types of proteins that will be phosphorylated at a particular point during the cell cycle

50. Cyclins and CDK’s • CDK levels don’t change while cyclins are destroyed at the end of each phase • There are 3 general groups of each • G1 cyclins • Cyclin D • S-phase cyclins • Cyclin A • G2 cyclins • Cyclin B (maturation promoting factor MPF) • Cyclin E is shared between G1 and M phase • Cyclin A is shared between M phase and G2