Cell Divison Mitosis and Meiosis

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					   Cell Division
Mitosis and Meiosis
           Types of Cell Division
1)    Mitosis
     occurs in all body cells (somatic cells) in
       animals, plants, and humans


        production of 2 identical daughter
         cells that are diploid

        growth or replacement of body cells.

        asexual reproduction. (offspring and
         parents are identical)
        Types of Cell Division
2) Meiosis
   occurs only is sex cells (sperm and
  egg)

   productionof the 4 non-identical
    gametes (sex cells) that are haploid

   Sperm  and eggs have half the genetic
    information

   sexual   reproduction
                  The Cell Cycle
   10% time dividing (mitotic phase/meiotic phase)
   90% time interphase (G1, S, G2 phases)
Interphase

1) G1 (gap phase) -manufactures proteins and
   amino acids needed for both cell processes
   and cell division, carries out metabolic duties
     Cell grows

  2) S phase (synthesis phase) – DNA
     replicates.
      -longest stage of the cell cycle
3) G2 (gap phase)
 increases the rate of protein synthesis
  and prepares to divide.
 grows larger
Division

        Mitosis or Meiosis

        cell can divide only about 50 times on
         average.

        To ensure that the cells in a tissue are
         healthy, cells will undergo a form of cell
         suicide called apoptosis.

   Cell Death
                    Terms
   Chromatin – complex long threads made
    of DNA and protein that makes up
    chromosomes

   Uncondensed chromosome – long, thin
    strands not visible with light microscope

   Condensed chromosome – short and
    visible
Chromosome vs. Chromatid
     Chromosomes replicate before division to
      form 2 matched sister chromatids
                        Ploidy
   Humans have 46 chromosomes (diploid or
    2N)

   Sex gametes have 23 chromosomes (haploid
    or N

   Some organisms have polyploidy
       Ex) corn – 4n (tetraploidy)
    Homologous chromosomes
–same size and shape and carry the genes for the
  same traits, but have different details
    Humans have 23 homologous chromosomes
     for a total of 46
Gene
  basic unit of heredity
  sequence of nucleotide bases in DNA.

  codes for a specific proteins
   Autosomes – chromosomes that do not
    influence gender (humans have 22 pairs of
    these)

   Sex Chromosomes – X and Y
    chromosomes that determine gender in
    humans (humans have 1 pair of these, the
    23rd chromosome pair)
Mitosis
                   Prophase
                (longest phase)
   Early: chromatin condenses to form
    chromosomes, centrioles move to poles
    and attach to spindle fibres

   Late: spindle fibres attach to centromere,
    nuclear membrane dissolves
                 Metaphase
   chromosomes line up on the equatorial
    plate (center of the nucleus)
                   Anaphase
   Spindle fibres contract from the centrioles
    and sister chromatids begin to separate
    apart, immediately chromosomes being to
    unravel
                 Telophase

   nucleolus re-appears, nuclear membrane
    reforms, the chromosomes unravel to form
    a loose mass of chromatin
   cells undergo cytokinesis (divide
    cytoplasm)
              Plant vs Animal Cells
   a cell plate forms      the cell membrane
    between the new          pinches in between
    daughter cells           the two daughter cells
                      Mitosis Overall
   http://www.loci.wisc.edu/outreach/bioclips/CDBio.html
  Some Methods of Asexual Reproduction

1. Binary fission - equal division of both the
  organism cytoplasm and nucleus to form two
  identical organisms

ex: Protist, amoeba
2) Budding - one parent dividing its nucleus
  (genetic material) equally, but cytoplasm
  unequally ex: Fungi- yeast
       Meiosis – Sexual Cell Division
 Occurs in sexual
reproduction

The end result is 4
gamates that are
genetically different

Spermatagonium
4 sperms

Oogonium 4 eggs
    Meiosis I – Reduction Division
Prophase I – homologous chromosomes
  undergo synapsis (pair up) and crossing
  over occurs.
-also, as in mitosis prophase:
Chromos condense
Nuclear membrane disappears
Centrioles move to opposite
poles
-tetrad
   Metaphase I – homologous pairs line up
    along the equatorial plate, spindles insert
    into the centromeres.
   Anaphase I – homologous chromosomes
    separate and are pulled to opposite poles
      = segregation
   Chromosomes undergo independent assortment
    in during Anaphase I
      -increases genetic diversity
   Telophase I – daughter cells separate,
    each has one chromosome from each
    homologous pair.
      -reduction has occurred so that the new cells
      will be haploid (n)
     -cytokinesis occurs
    Meiosis II – like mitosis but no initial
             replication of DNA
     -very brief, not as long as meiosis I
   Prophase II –spindles form
   Metaphase II –chromosomes align at the
    equatorial plate
   Anaphase II – the daughter chromatids
    separate and move towards separate
    poles
   Telophase II – spindle fibres disappear,
    nuclei reform and cytokinesis takes place.
    (All 4 daughter cells are haploid.)
How many genetic combinations
        of gamates?
   The number of possible chromosome
    combination in a gamate is 2^n
      Where ‘n’ is the haploid number

      Ex. Humans n=23, thus 2^23 =8, 388, 608
       different combinations!!

     Now   THAT’S diversity!!
   NOVA Online | 18 Ways to Make a Baby |
    How Cells Divide: Mitosis vs. Meiosis
    (Flash)
Human Life Cycle
Fern Life Cycle
Oogenesis
Spermatogenesis
        Oogenesis vs Spermatogenesis
   Oogenesis (female)             Spermatogenesis
                                    (male)
   meiosis II completes only      meiosis I and II are both
    if egg is fertilized            completed before
   Secondary oocyte                fertilization
    receives most of the           each sperm cell produced
    cytoplasm and becomes           receives an equal share
    the egg                         of cytoplasm
   polar bodies have less         flagellum forms from one
    cytoplasm and                   of the centrioles
    degenerate                     four spermatids are
   one egg cell is produced        produced
Human Karyotype Chart
             Gender


 Female  is XX
 Male is XY




                      XX   XY
   Chromosomal abnormalities can be
    detected by doing a karyotype chart.

   Fetal cells are collected through
    amniocentesis or chorionic villi
    sampling
    Successful cell division relies on 2
                  things:

1. accurate replication of the
    chromosomes
2. exact separation / distribution of the
    chromosomes
   Trisomy –three chromosomes
    replace a normal pair (47
    chromosomes in humans)
                Abnormal Meiosis
   Non-disjunction – occurs during
    meiosis when two homologous
    chromosomes move to the same pole.
    Chromosomes do not separate properly




        Normal Division      Non-disjunction
     Some Common Genetic Disorders
Down’s syndrome – trisomy 21
 Extra 21 chromosome



   more common in children born to women
    over 40

   characterized by short stature, folds to the
    eyelids, stubby fingers, wide gap between
    1st and 3rd toes, large fissured tongue,
    round head, palm creases, mild to severe
    mental retardation.
Edward’s syndrome – trisomy 18
 results in severe overall defects with a
  life expectance of only 10 weeks

Patau’s syndrome – trisomy 13
 results in non-functioning eyes, severe
  deficits and limited life expectancy.
Klinefelter’s syndrome – XXY male
 sterile males with underdeveloped
  testes, overdeveloped breast tissue and
  sub-normal intelligence
Metafemale – XXX female
 no obvious deficits however menstrual
  irregularities and early menopause are
  common, some have increase
  aggression

XYY male
 taller than normal, recurrent acne
 Monosomy   –one chromosome
 replaces a normal pair (45
 chromosomes in humans)
Turner’s syndrome – XO female
 females with short stature, broad chest,
  heart defects, lack of breasts and absence
  of sexual maturation and menstruation

Cri du Chat syndrome
 deletion of a portion of one copy of
  chromosome number 5, malformed face
  and head, short life
      Societal Issues of Cell Division

Cloning
 identical offspring are formed from a single
  cell or tissue of the parent. (similar to
  mitosis)

   when plants send out runners, when
    bacteria divide and in identical twins.
    How to Clone: (the quick and easy, yet not
              so successful way)
   Take an egg cell from an adult female and
    remove the nucleus (enucleation).

   Replace the nucleus with the nucleus from
    a body cell of the individual to be cloned.

(the cell must be toti-potent, or have its identity
    genes turned off) (you can use stem cells
    here)
   Zap it!!! (a little magic is required here)

   Implant the zygote or blastula into the
    mother’s uterus.

   Wait until the gestational period is up and
    voila!

   Click and Clone
                              Dolly
   1997-2003
   nucleus from udder cell put into egg cell
            Problems with cloning:
   some think it is wrong!!! (ethical issue)
   artificially cloned organisms seem to
    age faster
   it is very time and resource consuming
    and is not guaranteed to work
                      Cell Ageing

   the ends of the chromosomes, called
    telomeres, shorten each time a cell divides,
    and when they become critically short, the cell
    dies.

    Totipotent: when cells
    reach a certain number
    of divisions, or age,
    DNA begins to altered
                      Cancer

   abnormal, uncontrolled cell division.

   May be caused due to mutation of genes
     Tumour suppressor genes – suppress cell
      division. (mutation turns these off)
     Proto-oncogenes – stimulate cell division.
      (mutation turns these on)


   Telomeres do not shrink in cancerous cells
            Why is cancer bad
   Cancer cells do not participate in helping
    the body to function.

   Cancer cells require and take away
    nutrients

   Cancer cells can break away
    (metastasis) from the tumour mass and
    spread to other parts of the body.

   NOVA Online | Cancer Warrior | How Cancer Grows

				
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