1 / 55

Cytology

Cytology. 0. Cell Division -- The Cellular Basis of Reproduction and Inheritance. In sexual reproduction Fertilization of sperm and egg produces offspring In asexual reproduction Offspring are produced by a single parent, without the participation of sperm and egg. LM 340 .

michaelehill
Download Presentation

Cytology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cytology 0 Cell Division -- The Cellular Basis of Reproduction and Inheritance

  2. In sexual reproduction • Fertilization of sperm and egg produces offspring • In asexual reproduction • Offspring are produced by a single parent, without the participation of sperm and egg

  3. LM 340 CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION • 8.1 Like begets like, more or less • Some organisms reproduce asexually • And their offspring are genetic copies of the parent and of each other Figure 8.1A

  4. Other organisms reproduce sexually • Creating a variety of offspring Figure 8.1B

  5. 8.2 Cells arise only from preexisting cells • Cell division is at the heart of the reproduction of cells and organisms • Because cells come only from preexisting cells

  6. Prokaryotic chromosomes Colorized TEM 32,500 • 8.3 Prokaryotes reproduce by binary fission • Prokaryotic cells • Reproduce asexually by cell division Figure 8.3B

  7. Duplication of chromosomeand separation of copies 1 Continued elongation of thecell and movement of copies 2 Division intotwo daughter cells 3 • As the cell replicates its single chromosome, the copies move apart • And the growing membrane then divides the cells Plasmamembrane Prokaryoticchromosome Cell wall Figure 8.3A

  8. THE EUKARYOTIC CELL CYCLE AND MITOSIS • 8.4 The large, complex chromosomes of eukaryotes duplicate with each cell division • A eukaryotic cell has many more genes than a prokaryotic cell • And they are grouped into multiple chromosomes in the nucleus

  9. LM 600 • Individual chromosomes contain a very long DNA molecule associated with proteins • And are visible only when the cell is in theprocess of dividing • If a cell is not undergoing division • Chromosomesoccur in the form of thin, loosely packed chromatin fibers Figure 8.4A

  10. Sister chromatids Centromere TEM 36,000 • Before a cell starts dividing, the chromosomes replicate • Producing sister chromatids joined together at the centromere Figure 8.4B

  11. Chromosomeduplication Sisterchromatids Centromere Chromosomedistributiontodaughtercells • Cell division involves the separation of sister chromatids • And results in two daughter cells, each containing a complete and identical set of chromosomes Figure 8.4C

  12. INTERPHASE G1 S(DNA synthesis) G2 Cytokinesis Mitosis MITOTICPHASE (M) • 8.5 The cell cycle multiplies cells • The cell cycle consists of two major phases Figure 8.5

  13. During interphase • Chromosomesduplicate and new cellorganelles are made • During the mitotic phase • Duplicated chromosomes are evenly distributed into two daughter nuclei

  14. 8.6 Cell division is a continuum of changes • In mitosis, after the chromosomes coil up / condense • A mitotic spindle moves them to the middle of the cell

  15. The sister chromatids then separate • And move to opposite poles of the cell, where two nuclei form

  16. Cytokinesis, in which the cell divides in two (division of cytoplasm)

  17. The stages of cell division LM 250 INTERPHASE PROPHASE Late PROPHASE Centrosomes(with centriole pairs) Fragmentsof nuclearenvelope Centrosome Early mitoticspindle Chromatin Nucleolus Centromere Chromosome, consistingot two sister chromatids Spindlefibres Nuclearenvelope Plasmamembrane

  18. TELOPHASE AND CYTOKINESIS ANAPHASE METAPHASE Nucleolusforming Cleavagefurrow Metaphaseplate Daughterchromosomes Nuclearenvelopeforming Spindle Figure 8.6 (Part 2)

  19. Cleavagefurrow SEM 140 Cleavage begins Contracting ring ofmicrofilaments Daughter cells • 8.7 Cytokinesis differs for plant and animal cells • In animals • Cytokinesis occurs by a constriction of the cell (cleavage) Figure 8.7A

  20. Daughternucleus Cell plateforming Wall ofparent cell TEM 7,500 Cell wall New cell wall Vesicles containingcell wall material Cell plate Daughter cells • In plants • A new cell wall form splits the cell in two Figure 8.7B

  21. CONNECTION • 8.10 Growing out of control, cancer cells produces malignant tumors • Cancer cells • divide excessively to form masses called tumors

  22. Lymphvessels Tumor Bloodvessel Glandulartissue Cancer cells invadeneighboring tissue. Cancer cells spread throughlymph and blood vessels toother parts of the body. A tumor grows from asingle cancer cell. • Malignant tumors • Can invade other tissues Figure 8.10

  23. Radiation and chemotherapy • Are effective as cancer treatments because they interfere with cell division

  24. LM 500 • 8.11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction • When the cell cycle operates normally, mitotic cell division functions in • Growth Figure 8.11A

  25. LM 700 • Replacement of damaged or lost cells Figure 8.11B

  26. LM 10 • Asexual reproduction Figure 8.11C

  27. MEIOSIS AND CROSSING OVER • 8.12 Chromosomes are matched in homologous pairs • The somatic (body) cells of each species • Contain a specific number of chromosomes • For example human cells have 46 • Making up 23 pairs of homologous chromosomes

  28. Chromosomes Centromere Sister chromatids • The chromosomes of a homologous pair • Carry genes for the same characteristics at the same place, or locus Figure 8.12

  29. 8.13 Gametes have a single set of chromosomes • Cells with two sets of chromosomes • Are said to be diploid • Gametes, eggs and sperm, are haploid • With a single set of chromosomes

  30. Haploid gametes (n = 23) n Eggcell n Spermcell Meiosis Fertilization Diploidzygote(2n = 46) 2n Multicellulardiploid adults(2n = 46) Mitosisand development • Sexual life cycles • Involve the alternation ofhaploid and diploid stages Figure 8.13

  31. 8.14 Meiosis reduces the chromosome number from diploid to haploid • Meiosis, like mitosis • Is preceded by chromosome duplication • But in meiosis • The cell divides twice to form four daughter cells

  32. The first division, meiosis I • Starts with synapsis, the pairing of homologous chromosomes • Meiosis I separateseachhomologouspair • And produce two daughter cells, each with one set of chromosomes

  33. Meiosis II is essentially the same as mitosis • The sister chromatids of each chromosome separate • The result is a total of four haploid cells

  34. MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Sister chromatids remain attached Microtubulesattached to kinetochore Centrosomes (with centriole pairs) Metaphaseplate Sites of crossing over Spindle Centromere Homologouschromosomes separate Sisterchromatids Nuclearenvelope Tetrad Chromatin • The stages of meiosis Figure 8.14 (Part 1)

  35. MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploid daughter cellsforming Figure 8.14 (Part 2)

  36. Mitosis Meiosis Parent cell(before chromosome replication) Meiosis i Prophase I Prophase Tetrad formedby synapsis ofhomologouschromosomes Chromosome replication Chromosome replication Duplicated chromosome(two sister chromatids) 2n = 4 Chromosomes align at themetaphase plate Tetradsalign at themetaphase plate Metaphase I Metaphase Anaphase ITelophase I Homologous chromosomesseparate duringanaphase I;sister chromatidsremain together Sister chromatidsseparate during anaphase AnaphaseTelophase Haploidn = 2 Daughtercells of meiosis I No furtherchromosomalreplication; sisterchromatids separateduringanaphase II Meiosis ii 2n 2n Daughter cellsof mitosis n n n n Daughter cells of meiosis II • 8.15 Review: A comparison of mitosis and meiosis Figure 8.15

  37. 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring • Each chromosome of a homologous pair • Differs at many points from the other member of the pair

  38. Possibility 1 Possibility 2 Two equally probablearrangements of chromosomes at metaphase I Metaphase II Gametes Combination 2 Combination 4 Combination 1 Combination 3 • Random arrangements of chromosome pairs at metaphase I of meiosis • Lead to many different combinations of chromosomes in eggs and sperm Figure 8.16

  39. Randomfertilization of eggs by sperm • Greatly increases this variation

  40. White coat (C); pink eyes (e) Brown coat (C); black eyes (E) Eye-colorgenes Coat-colorgenes Brown Black C E C E C E Meiosis c e c e Pink White c e Tetrad in parent cell(homologous pair ofduplicated chromosomes) Chromosomes of the four gametes • 8.17 Homologous chromosomes carry different versions of genes • The differences between homologous chromosomes • Are based on the fact that they can bear different versions of a gene at corresponding loci Figure 8.17A

  41. TEM 2,200 Chiasma Tetrad Centromere • 8.18 Crossing over further increases genetic variability • Genetic recombination • Which results from crossing over during prophase I of meiosis, increases variation still further Figure 8.18A

  42. Coat-colorgenes Eye-colorgenes Breakage of homologous chromatids 1 Joining of homologous chromatids 2 Separation of homologous chromosomes at anaphase I 3 Separation of chromatids at anaphase II and completion of meiosis 4 • How crossing over leads to genetic variation E C Tetrad (homologous pair of chromosomes in synapsis) e c E C e c E C Chiasma e c E C e C E c e c E C Parental type of chromosome e C Recombinant chromosome E c Recombinant chromosome e c Parental type of chromosome Gametes of four genetic types Figure 8.18B

  43. New combination of genes in recombinant chromosomes

  44. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE • 8.19 A karyotype is a photographic inventory of an individual’s chromosomes • A karyotype • Is an ordered arrangement of a cell’s chromosomes

  45. Hypotonicsolution Fixative Packed red andwhite blood cells Stain White blood cells Centrifuge Blood culture Another centrifugation step separates the swollen whiteblood cells. The fluid containing the remnants of the red blood cells is poured off. A fixative (preservative) is mixedwith the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried, and stained. 1 2 The fluid is discarded, and a hypotonic solution is mixed with the cells. This makes the red blood cells burst. The white blood cells swell but do not burst, and their chromosomes spread out. A bloodculture is centrifuged to separate the blood cells from the culture fluid. Fluid 3 Centromere Sisterchromosomes Pair of homologouschromosomes 2,600X The resulting display is the karyotype. The 46 chromosomes here include 22 pair of autosomes and 2 sex chromosomes, X and Y. Although difficult to discern in the karyotype, each of the chromosomes consists of two sister chromatids lying very close together (see diagram). 5 The slide is viewed with a microscope equipped with a digital camera. A photograph of the chromosomes is entered into a computer, which electronically arranges them by size and shape. 4 Preparation of a karyotype from a blood sample Figure 8.19

  46. CONNECTION • 8.20 An extra copy of chromosome 21 causes Down syndrome • A person may have an abnormal number of chromosomes • Which causes problems

  47. 5,000 • Down syndrome is caused by trisomy 21 • An extra copy of chromosome 21 Figure 8.20A Figure 8.20B

  48. 90 80 70 60 Infants with Down syndrome (per 1,000 births) 50 40 30 20 10 0 35 40 50 20 25 30 45 Age of mother • The chance of having a Down syndrome child • Goes up with maternal age Figure 8.20C

  49. 8.21 Accidents during meiosis can alter chromosome number • Abnormal chromosome count is a result of nondisjunction • The failure of homologous pairs to separate during meiosis I • The failure of sister chromatids to separate during meiosis II

  50. Nondisjunction in meiosis I Normal meiosis I Normal meiosis II Nondisjunction in meiosis II Gametes Gametes n n + 1 n -1 n n + 1 n + 1 n 1 n 1 Number of chromosomes Number of chromosomes 0 Figure 8.21B Figure 8.21A

More Related