Law of inheritance Proposed genetic factors - PowerPoint PPT Presentation

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Law of inheritance Proposed genetic factors

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  1. Law of inheritance Proposed genetic factors Chromosomal theory Real observation of division of genetic elements extentions Mitosis and meiosis Cell cycle Genetic analysis Aneuploid Recombination Gene conversion

  2. Evidence that Genes Reside in the Nucleus • 1667 – Anton van Leeuwenhoek • Microscopist • Semen contains spermatozoa (sperm animals) • Hypothesized that sperm enter egg to achieve fertilization • 1854-1874 – confirmation of fertilization through union of eggs and sperm • Recorded frog and sea urchin fertilization using microscopy and time-lapse drawings and micrographs

  3. Evidence that Genes Reside in Chromosomes • 1880s – innovations in microscopy and staining techniques identified thread-like structures • Provided a means to follow movement of chromosomes during cell division • Mitosis – two daughter cells contained same number of chromosomes as parent cell (somatic cells) • Meiosis – daughter cells contained half the number of chromosomes as the parents (sperm and eggs)

  4. Chromosomal theory Pangenesis A gradual process Key observation 1883 E. van Beneden Hippocrates (460-350 BC) 19th century The egg and sperm contributes equal number of chromosomes to the fertilized egg

  5. Boveri Centriols of ascaris

  6. Reproduction as the basis of heredity Cells – prokaryotes, eukaryotes ( with membrane-bound organelles) Chromosomes Mitosis (mitox-thread)– cell cycle, cell division Meiosis (meiwsix-reduction) – oogenesis and spermatogenesis - meiosis in plants Life cycle Principle of Genetics Chapter 2 Cell 112:423-440 2003

  7. DNA Deviding E.coli An interphase eukaryotic cells

  8. Cell division *proper distribution of genetic materials into daughter cells - separation of chromosomes • Chromosomes • Transmission of genetic materials • orderly releases of genetic information ( gene regulation) The structure of replicated chromosome

  9. order cell mass Duplication of genetic material Division for equal distribution of genetic material The cell cycle ( mammalian cells in tissue culture)

  10. The mitotic spindle in a cultured animal cell Centrosome (MTOC) asters Centriols (surrounded by pericentriolar material –initiation of formation of the microtubules)

  11. Time Events Coordination Mitosis cytokinesis Identical daughter cells Parental cells 2n  2n Daughter cells

  12. Three-Dimensional Maps of All Chromosomes in Human Male Fibroblast Nuclei and Prometaphase Rosettes (PLoS Biol. 2005 May;3(5):e157. Epub 2005 Apr 26. ) chromatin Chromosome (condensed)

  13. cytokinesis Animal cells A cleavage furrow Plant cells: Formation of a cell plate

  14. Chromosome : sister chromatid cohesion and separation (cohesin) chromosomal condensation and decondensation (condensins, topoisomerase II) Microtubules : spindle formation (cetrosomes, asters) Microtubule – chromosome interaction: kinetochore formation

  15. Meiosis

  16. Meiosis 1883 Edouard van Beneden # of chromosome Eggs of round worm = ½ somatic cells Zygonema Pairing Homologous chromosomes **synapsis crossing over 1st meiotic division - reduction division (separation of homologous chromosomes) 2nd meiotic division - equatorial division (separation of sister chromatid)

  17. Crossing over The synaptinemal complex

  18. chiasmatas disappearance of synaptal complex **synapsis crossing over chromomeres towards the center of nucleus

  19. Chiasmata

  20. Life cycle – the sequence of events from fertilization to death a few examples Neurospora crassa One gene – one enzyme 1st meiotic division 2nd meiotic division Ordered meiosis

  21. Saccharomyces cerevisiae Easy to grow, easy to manipulate

  22. Meiosis and mitosis in plants Meiosis  gametogenesis

  23. Drosophila melanogaster

  24. Beyond meiosis Hormone effect With meiotic program Early embryologenesis Diplotene diplonema After puberty After puberty 1/month Asymtrical cytokinesis differentiation Unequal distribution of cytoplasm differentiation nonmotile spermatogenesis Oogenesis in female