Genetics Chapter 3.ppt
- 2. Acknowledgment ? Addis Ababa University ? Jimma University ? Hawassa University ? Haramaya University ? University of Gondor ? American Society of Clinical Pathologists (ASCP) ? Center for Disease Control-Ethiopia (CDC- Ethiopia)
- 3. Course objective of mitosis At the end of this chapter, the students will be able to ? Explain the importance of cell division ? Discuss about cell cycle stage in mitosis (interphase, and mitosis) ? Describe the characteristic features of the four developmental stages of mitosis ( Prophase, metaphase, anaphase, and telophase) ? Discuss about cell cycle control mechanisms
- 5. ? One purpose of cell division is asexual reproduction ¨C This is the means by which some unicellular organisms produce the next generation of the organism ¨C Examples ? Bacteria ? Amoeba ? Yeast ¨C Saccharomyces cerevisiae (Baker¡¯s yeas 3.2 CELLULAR DIVISION
- 6. ? A second purpose for asexual reproduction is to produce multi-celled organisms and to enable these organisms to grow and repair damaged tissue ¨C Plants, animals and certain fungi are derived from a single cell that has undergone repeated asexual cell divisions ¨C For example ? Humans start out as a single fertilized egg ? End up as an adult with several trillion cells 3.2 CELLULAR DIVISION
- 7. Prokaryotes Reproduce Asexually by Binary Fission ? The capacity of bacteria to divide is really quite astounding ¨C Escherichia coli, for example, can divide every 20 minutes ? Prior to division, the bacterial cell replicates its chromosome ? Then the cell divides into two daughter cells by a process termed binary fission
- 8. Figure 3.4
- 9. A Generalized Cell Golgi body Nuclear envelope Chromosomal DNA Nucleus Nucleolus Polyribosomes Ribosome Rough ER Cytoplasm Membrane protein Plasma membrane Smooth ER Mitochondrion Centrioles Microtubules Microfilaments Lysosome (b) Animal cell
- 10. Cell division Cell division composed of two processes: ? Nuclear division (Karyokinesis)-that includes mitosis, and meiosis ? Cytoplasm division (Cytokinesis
- 11. ? Kinotochores-are the attachment points of the sister chromatides, and the constriction in the chromosome where the attachment occur, are called centromers. ? Chromosomes may grouped, according to the position of the centromers as: - Metacentric: where centromers are in the middle of chromosomes - Telocentric: where centromers are in the end of chromosomes - Acrocentric: where centromers are in the very end of chromosomes - Other terminologies include: subtelocentric, or submetacentric
- 13. ? Karyotype: the total chromosome complement of a cell ? Ideogram: a photograph that showmitotic division, and the rearrangement of pair of chromosomes
- 14. Chromosomes ? Key features of a chromosome: centromere (where spindle attaches), telomeres (special structures at the ends), arms (the bulk of the DNA). ? Chromosomes come in 2 forms, depending on the stage of the cell cycle. The monad form consists of a single chromatid, a single piece of DNA containing a centromere and telomeres at the ends. The dyad form consists of 2 identical chromatids (sister chromatids) attached together at the centromere. ? Chromosomes are in the dyad form before mitosis, and in the monad form after mitosis. ? The dyad form is the result of DNA replication: a single piece of DNA (the monad chromosome) replicated to form 2 identical DNA molecules (the 2 chromatids of the dyad chromosome).
- 15. More Chromosomes ? Diploid organisms have 2 copies of each chromosome, one from each parent. The two members of a pair of chromosomes are called homologues. ? Each species has a characteristic number of chromosomes, its haploid number n. Humans have n=23, that is, we have 23 pairs of chromosomes. Drosophila have n=4, 4 pairs of chromosomes.
- 16. Cell Cycle ? The cell cycle is a theoretical concept that defines the state of the cell relative to cell division. ? The 4 stages are: G1, S, G2, and M. ? M = mitosis, where the cell divides into 2 daughter cells. The chromosomes go from the dyad (2 chromatid) form to the monad (1 chromatid) form. That is, before mitosis there is 1 cell with dyad chromosomes, and after mitosis there are 2 cells with monad chromosomes in each. ? S = DNA synthesis. Chromosomes go from monad to dyad. ? G1 = ¡°gap¡±. Nothing visible in the microscope, but this is where the cell spends most of its time, performing its tasks as a cell. Monad chromosomes ? G2 (also ¡°gap¡±). Dyad chromosomes, cell getting ready for mitosis. ? G1, S, and G2 are collectively called ¡°interphase¡±, the time between mitoses
- 17. The Cell Cycle G1 G2 S Two daughter cells M Mitosis Interphase Gap 1 Gap 2 Synthesis Growth Gene expression Differentiation DNA Synthesis Gene expression Quality control Actual division process
- 18. ? At the end of S phase, a cell has twice as many chromatids as there were chromosomes in G1 phase ¨C i.e. - human cell ? 46 chromosomes in G1 phase ? 46 pairs of sister chromatids in G2 phase ? chromosome is therefore a relative term ¨C In G1, anaphase, & telophase it refers to the equivalent of one chromatid ¨C In G2, prophase, & metaphase, it refers to a pair of sister chromatids Chromatids, Chromosomes¡ What the¡
- 19. Interphase ? Chromosomes are decondensed ? chromosomes replicate ? The centrosome divides Nuclear membrane Chromosomes Two centrosomes, each with centriole pairs
- 20. Mitosis ? Comes from the Greek word for ¡° a thread¡± referring to chromosome. ? Mitosis is a continuous process. However, for descriptive purpose it is broken into four stages: prophase,metaphase, anaphase, and telophase.(Greek-pro-before; meta-mid; ana-back, and telo-end). ? The timing for the four stagesin the cell cycle(G1, S, G2, and M) varies from species to species, from organ to organ with in a species, even from cell to cell with in a given cell.
- 21. ? Mitosis is subdivided into four phases ¨CProphase ¨CMetaphase ¨CAnaphase ¨CTelophase
- 22. Prophase ? chromosomes condense (become short and thickened) so that individual chromosomes become distinct ? Nuclear envelope disintegrate ? Centrosomes move to opposite poles ? mitotic spindle apparatus forms ? nuclear envelope disappears Microtubules forming mitotic spindle Sister chromatids Centromere
- 23. METAPHASE ? Spindle fibers attached to the individual chromosomes at their kinetochores ? Chromosomes are positioned in the plane of equator of the spindle, called metaphase plate Astral microtubule Metaphase plate Kinetochore proteins attached to centromere Kinetochore microtubule Polar microtubule
- 24. Spindle Apparatus ? Composed of microtubules originated from centrioles ? Microtubules are formed polymerization of tubulin proteins ? 3 types of spindle microtubules ¨C Aster microtubules ? Important for positioning of the spindle apparatus ¨C Polar microtubules ? Help to ¡°push¡± the poles away from each other ¨C Kinetochore microtubules ? Attach to kinetochore , at the centromere
- 26. ? Spindle fibers bind kinetochores ? The two kinetochores on a pair of sister chromatids are attached to kinetochore MTs from opposite poles Nuclear membrane fragmenting Spindle pole Mitotic spindle
- 27. Metaphase ? Pairs of sister chromatids align themselves at the metaphase plate Polar microtubule Kinetochore proteins attached to centromere Kinetochore microtubule Astral microtubule Metaphase plate
- 28. Anaphase ? Centromeres separate ? Each chromatid, is linked to only one pole ? As anaphase proceeds ¨C Kinetochore MTs shorten ? Chromosomes move to opposite poles ¨C Polar MTs lengthen ? Poles themselves move further away from each other Chromosomes
- 29. Telophase & Cytokinesis ? Chromosomes reach poles & decondense ? Nuclear membrane reforms ? Quickly followed by cytokinesis ¨C In animals ? Formation of a cleavage furrow ¨C In plants ? Formation of a cell plate
- 30. Telophase cytokinesis: cytoplasm divided into 2 separate cells --chromosomes de-condense --nuclear envelope re-forms --spindle vanishes
- 31. Control of cell cycle Cell cycle controlled by proteins found in the cytoplasm. Of these, principle ones include: A) Cyclines:-cyclin D (G1 cyclin) - cyclins E &A (S phase cyclin) - cyclines B &A (mitotic cyclins) Levels of cyclines rise and fall with the stage of cell cycle
- 32. Controlling of cell cycle, continued B) Cyclin-dependant kinases (CDKs) - CDK 4, a G1 CDK - CDK 2, an S-phase CDK - CDK 1, an M phase CDK ? CDK¡¯s level remain fairly stable, and activated when combined with respective cyclin ? CDK added phosphate group to variety of protein substrates that control cell cycle
- 33. ? Mitosis ultimately produces two daughter cells genetically identical to the mother cell ¨C Barring rare mutations ? Processes requiring mitotic cell division ¨C Development of multicellularity ¨C Organismal growth ¨C Wound repair ¨C Tissue regeneration Some Key Points
- 34. Controlling of cell cycle, continued The anaphase-promoting complex (APC, also called cyclosome, & so designed as APC/C) -triggers the events leading to destruction of the cohesions thus allowing the sister chromatids to separate -degrades the mitotic cyclin B
- 35. Summery questions 1. Explain the importance of cell cycle on the life of an organism 2. Discuss the function of at least 5 organelles of the cells 3. Define the term: kinotochore, metacentrics, telocentric, acrocentric and ideogram 4. Explain the characteristic feature of the cell at G1, S, and G2 interphase stages 5. Explain the characteristic feature of mitosis developmental stages (prophase, metaphase, anaphases, and telophase) 6. Explain about control mechanisms mitotic cell division
- 36. Meiotic Cell Division Part II
- 37. Course objective of meiosis At the end of the course, the students will be able to ? Describe developmental stages in meiosis ? Explain the difference between mitosis and meiosis ? Discuss about spermatogenesis ? Discuss about oogenesis
- 38. ? Sexual reproduction is the most common way for eukaryotic organisms to produce offspring ? Parents make gametes with half the amount of genetic material (haploid) ? These gametes fuse with each other during fertilization to generate a new organism Sexual Reproduction
- 39. ? Simple eukaryotes are isogamous ¨C They produce gametes that are morphologically similar ? Most eukaryotic species are heterogamous ¨C These produce gametes that are morphologically different ? Sperm cells ¨C Relatively small and mobile ? Oocytes or ova ¨C Usually large and nonmobile ¨C Store large amounts of nutrients ? Microspores (Pollen) ? Macrospores (Ovules) Gametes
- 40. How Does One Make a Haploid Gamete? ? Answer ¨C meiosis ? Haploid cells are produced from diploid cells during gametogenesis ? The chromosomes must be distributed to reduce the chromosome number to half its original value ? but simultaneously sorted to assure that each chromosome (& its genes) is represented in each gamete
- 41. ? Meiosis begins after a cell has progressed through G1, S, & G2 ? Meiosis involves two successive divisions ¨C Meiosis I and II ¨C Each of these is subdivided into ? Prophase ? Metaphase ? Anaphase ? Telophase 3-44 Meiosis
- 42. Meiosis ? Prophase I is further subdivided into periods known as ¨C Leptotena ¨C Zygotena ¨C Pachytena ¨C Diplotena ¨C Diakinesis
- 43. A recognition A total of 4 chromatids Figure 3.11 Periods of Prophase I
- 45. A physical exchange A tetrad 2 bivalent s Periods of Prophase I
- 46. Spindle apparatus complete; pairs of chromatids attached to kinetochore microtubules Stages of Meiosis I
- 47. ? Bivalents are organized along the metaphase plate ? Homologous pairs of sister chromatids aligned side by side ¨C A pair of sister chromatids is linked to one of the poles ¨C And the homologous pair is linked to the opposite pole ¨C The arrangement is random with regards to the (blue and red) homologues Figure 3.13
- 48. 3-50 Pairs of sister chromatids separate from each other The centromere remains between sister chromatids Stages of Meiosis I
- 49. Meiosis ? Telophase I & cytokinesis of meiosis I followed by meiosis II ? Meiosis I has reduced the number of chromosomes in the daughter cells to the ? the diploid number ? However, each homolog is still composed of 2 recombinant sister chromatids ¨C The genetic content is still 2n ? Meiosis II reduces the genetic content to n
- 50. Stages of Meiosis II 1 of each type of chromosome (n) in each daughter cell (gamete)
- 51. Mitosis vs Meiosis ? Produces two diploid daughter cells ? Produces daughter cells that ARE genetically identical ? Produce four haploid daughter cells ? Produces daughter cells that are NOT genetically identical
- 52. Separation of Alleles During Meiosis Prophase I Metaphase I Anaphase I Telophase I Meiosis II Haploid cells Heterozygous (Yy) cell from a plant with yellow seeds y y y y y y y Y Y Y Y Y Y Y
- 53. Meiosis I Meiosis II or 2 Ry : : Heterozygous diploid cell (YyRr) to undergo meiosis y y y y y y y y y Y Y Y Y Y Y Y Y Y R R R r r y r r R R Y R R R R y R r r r r Y r Y y R r R r r 2 rY 2 ry 2 RY Separation of Alleles During Meiosis
- 54. Spermatogenesis ? The production of sperm ? In male animals, it occurs in the testes ? A diploid spermatogonium cell divides mitotically to produce two cells ¨C One remains a spermatogonial cell ¨C The other becomes a primary spermatocyte ? The primary spermatocyte progresses through meiosis I and II ¨C Refer to Figure 3.14a
- 55. 3-55 Copyright ?The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 3.14 (a) Meiois I yields two haploid secondary spermatocyte s Meiois II yields four haploid spermatids Each spermatid matures into a haploid sperm cell
- 56. 3-56 ? The structure of a sperm includes ¨C A long flagellum ¨C A head ? The head contains a haploid nucleus ¨C Capped by the acrosome Copyright ?The McGraw-Hill Companies, Inc. Permission required for reproduction or display The acrosome contains digestive enzymes - Enable the sperm to penetrate the protective layers of the egg ? In human males, spermatogenesis is a continuous process ? A mature human male produces several hundred million sperm per day
- 57. Oogenesis ? The production of egg cells ? In female animals, it occurs in the ovaries ? Early in development, diploid oogonia produce diploid primary oocytes ¨C In humans, for example, about 1 million primary occytes per ovary are produced before birth 3-57 Copyright ?The McGraw-Hill Companies, Inc. Permission required for reproduction or display
- 58. ? The primary oocytes initiate meiosis I ? However, they enter into a dormant phase ¨C They are arrested in prophase I until the female becomes sexually mature ? At puberty, primary oocytes are periodically activated to progress through meiosis I ¨C In humans, one oocyte per month is activated ? The division in meiosis I is asymmetric producing two haploid cells of unequal size ¨C A large secondary oocyte ¨C A small polar body 3-58 Copyright ?The McGraw-Hill Companies, Inc. Permission required for reproduction or display
- 59. ? The secondary oocyte enters meiosis II but is quickly arrested in it ? It is released into the oviduct ¨C An event called ovulation ? If the secondary oocyte is fertilized ¨C Meiosis II is completed ¨C A haploid egg and a second polar body are produced ? The haploid egg and sperm nuclei then fuse to created the diploid nucleus of a new individual
- 60. Summery questions 1. What is the importance of meiotic cell division? 2. Explain the developmental stages of meiosis cell division 3. What is the difference between mitotic and meiotic cell division 4. What is the similarity and differences between spermatogenesis and oogenesis.
- 61. Reference ? Robert F. weaver, Philip W. Hedrick. Genetics. ? Darnel, Lodish, Baltimore. Molecular Cell Biology ? James D. Watson: Recombinant DNA ? Robert F. Weaver. Molecular biology ? Benjamin Lewin: Genes VI and above
- 62. Reference continued¡. ? Richard J. Epistein: Human Molecular Biology ? P.K. Gupta: Cell and Molecular Biology ? Vertualtext erigito.com/Molecular biology www.ergito.com ? http://www.emporia.edu/biosci/genetics/notegen e.html ? http://www.biol.wwu.edu/young/321_07a.html