3.2- sexual reproduction and cell specialization

Why sexual reproduction?
1. Is the production of a new individual
2. Joining of two gametes
  1. Haploid cells
  2. Form zygote
  3. Male
    1. Many, mini, motile
    2. In animals
      1. Testes
        Produce spermatozoa (sperm)
    3. In plants
      1. Anthers
        Produce pollen
  4. Female
    1. Few, fat, fixed
    2. In plants
      1. Ovaries
        Produce ovules
    3. In animals
      1. Ovaries
        Produce ova (eggs)
3. Not genetically the same
  1. Contain genetic info from both parents
4. Increases genetic variety
  1. Increase chance of surviving
Using totipotent cells
1. Plant cells
  1. Easy to clone
  2. Remain totipotent throughout life
  3. Single cells can be grown in a rich nutritive medium
2. Animal cells
  1. Embryo splitting
    1. Every cell in early embryo is totipotent
    2. Take embryos from the best stock
    3. Separate embryo into individual cells
    4. Put in rabbits for shipment
    5. Embryos placed in seragate mothers
What causes cell differentiation
1. Cells switch genes on nd off
2. Restoring totipotency
  1. Cloning animals is difficult because cells no longer totipotent
  2. Many dificulties with this technique
    1. Difficult to culture
Embryo development and cell differentiation
1. Totipotent
  1. Can form any cell type
2. After fertilisation
  1. Cleavage
    1. Repeated mitosis
    2. Form blastocyst
      1. Mass of small undifereciated cells
3. Pluripotent
  1. Can form all cells appart from tissue (placenta)
Meiosis
1. A reduction division
2. Interphase
  1. Prophase 1
    1. Metaphase 1
      1. Anaphase 1
        Telophase 1
        Metaphase 2
        Anaphase 2
        Telophase 2
        Nuclear envelopes reform
        Chromosomes return to interphase state
        4 daughter cells half the chromosomes
        centromeres divide
        Chromatids move to opps ends
        New spindles formed
        Chromosomes line on equator
        Nuclear membrane reforms
        Brief interphase NO replication
        Centromeres DON'T divide
        One chromosome from each moves to side of cell
      2. Spindle fibers form
      3. Pairs of chromasomes line on equator
      4. Crossing over occurs
        Multienzymes 'cut and stick' bits together
        Chiasmata- Points where chromatids break
    2. Coil and condensed form
    3. 2 chromatids
3. Half chromosomes number
4. 4 daughter cells
Fertilisation
1. Humans
  1. Digestive enzymes pour out acrosome
    1. Digest zona pellucida
      1. Sperm touches oocyte
        Membranes fuse
        Nucleus released
        Decondenses and releases chromosomes
        Oocyte releases cortical granules
        Combine wid zona pellucida
        Form tough fertilization membrane
2. Plants
  1. Pollen tube nucleus grows a tube
    1. This enters the ovule then degenerates
      1. 1 male gamete fuses wid polar bodies
        The other fues with female gamete
        Produces diploid zygote
        Produce triploid endosperm nucleus
Gametogenesis
1. Humans
  1. Oogenesis
    1. Primordial germ cell
      1. Mitosis twice
        4 oogonia
        Grow into primary oocyte
        Meiosis 1
        1 secondary oocyte
        Meiosis 2
        1 Ovum
        Cytoplasm with food reserves
        Cell surface membrane
        Jelly like layer-zona pellucida
        1 polar body (dies)
        1 polar body(may not divide)
        2 polar bodies (die)
  2. Spermatogenesis
    1. Primordial germ cell
      1. Mitosis twice
        4 spermotogonia
        Grow into primary spermotocyte
        Meiosis 1
        2 secondary spermatocytes each
        Meiosis 2
        4 spermatids
        4 spermatozoa (sperm)
        Acrosome- storage site for digestive enzyme
        Nucleus-contains chromosomes
        Mitochondria-provide energy for tail
        Microtubules-produce whip like movement
2. Plants
  1. Megagametogenesis
    1. Megaspore mother cell
      1. Meiosis twice
        4 haploid cells
        3 degenerate
        Growth
        Megaspore
        3 mitosis
        Mature embryo sac
        3 antipodal cells
        2 polar nuclei
        2 synergids
        Female gamete
  2. Microgametogenesis
    1. Microspore moX, ther cell
      1. Meiosis twice
        4 haploid cells
        Mitosis
        Pollen grain (microspore)
        Pollination
        Pollen grain on a stigma
        Mitosis of generative nucleus
        Pollen tube nucleus
        Generative nucleus

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3.2- sexual reproduction and cell specialization

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	Creado por victoria.graham96 hace casi 11 años