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Chromosomes and Mitosis

Chromosomes and Mitosis. Lecture 6. 1 Chromosomal Basis of Heredity. A gene is a unit of heredity Genes are carried on DNA DNA is contained within chromosomes as chromatin. Chromosomes replicate during cell division. The chromosome complement. Chromosome analysis.

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Chromosomes and Mitosis

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  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

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