Exercise 8: Mitosis and Meiosis

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Exercise 8 Mitosis and Meiosis
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Cell Division

• All living organisms are composed of one or more
  cells.
• The cell is the smallest unit having the
  properties of life.
• The continuity of life arises directly from the
  growth and division of single cells.

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Cell Division

• Parent cells must give their daughter cells
  specific hereditary instructions and enough
  metabolic machinery to continue live.
• DNA is the hereditary material and the metabolic
  machinery is housed in the cytoplasm.

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Cell Division

• In order for a eukaryotic cell to divide, it must
  undergo nuclear division and cytoplasmic division
• There are two nuclear division mechanisms
  Mitosis and Meiosis.
• Mitosis occurs in somatic cells and in single
  celled organisms that undergo asexual
  reproduction.
• Meiosis occurs in germ cells and in single celled
  organisms that reproduce sexually.

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The Cell Cycle

• Cells divide by going through an orderly sequence
  of events called the Cell Cycle.
• The Cell Cycle has 4 stages G1, S, G2, and M.
• G1 first growth stage
• S Synthesis stage (DNA duplication occurs)
• G2 second growth stage
• M Mitosis and Cytoplasmic Division occur

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Interphase
G1
S
Telophase
Anaphase
Mitosis
G2
Metaphase
Prophase
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chromosome (unduplicated) in cell at interphase
same chromosome (duplicated) in interphase prior
to mitosis
Mitosis, Cytoplasmic Division
chromosome (unduplicated) in daughter cell at
interphase
chromosome (unduplicated) in daughter cell at
interphase
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Mitosis

• Mitosis is divided into 4 phases Prophase,
  Metaphase, Anaphase, and Telophase.
• Prophase Chromosomes condense and nuclear
  membrane breaks down.
• Metaphase chromosomes line up at spindle
  equator (cell center) and spindle fibers attach
• Anaphase Sister chromatids are separated
• Telophase Two clusters of chromosomes are
  present and nuclear membranes form around each.

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G1, S, G2
Mitosis
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End of Mitosis
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Cytokinesis

• After Mitosis is over, the cytoplasm is divided
  in a process called Cytokinesis.

Interphase
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Cytokinesis

• There are two mechanism of cytokinesis.
• 1. Cell Plate formation Plant Cells
• 2. Cleavage Furrow formation Animal Cells

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Plant Cell
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Animal Cell
Mitosis is over, and the spindle is now
disassembling.
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Lab Exercise

• Complete part 3 of the Mendelian genetics lab
  (count fruit flies).
• Complete sections on the Cell Cycle, Mitosis,
  Animal cell mitosis, Plant cell mitosis, and
  Cytokinesis (Exercise 8 section 1).
• Complete the 10 remaining lab drawings using
  prepared slides.

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Meiosis

• Meiosis Cell division mechanism that occurs in
  Germ Cells and organisms that reproduce Sexually.
• Germ Cells are the cells of an organism that are
  set aside to produce Gametes (Sex Cells).
• Sexual Reproduction produces offspring with
  genetic variations.
• Meiosis, the formation of Gametes, and
  Fertilization are the basic events of sexual
  reproduction.
• During Fertilization, the nuclei of two gametes
  join together.

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Germ Cells and Gametes
Human Male
Human Female
vagina
penis
testis (where sperm originates)
ovary (where eggs develop)
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Genetic Variation

• The cells of most sexual reproducers contain
  pairs of genes on pairs of Homologous
  Chromosomes.
• Homologous chromosomes carry the same sets of
  genes. One chromosome of the pair is Maternal
  and the other is Paternal.
• Variation in traits exists because these pairs of
  genes on these pairs of chromosomes might not be
  identical.
• Different versions of the same gene are called
  Alleles.
• The reason that sexual reproducers do not all
  look alike is that they inherit new combinations
  of alleles.

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Meiosis

• During Meiosis the chromosome number is cut in
  half.
• Germ cells start out with the same chromosome
  number as somatic cells. (2n in diploid
  organisms). The gametes that are produced by
  germ cells only contain half of that (n).

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Meiosis

• Meiosis is similar to Mitosis in that Interphase
  Prophase, Metaphase, Anaphase, and Telophase take
  place.
• However, unlike Mitosis, during Meiosis these
  phases (except Interphase) occur twice (Meiosis I
  and Meiosis II).

MEIOSIS I
MEIOSIS II
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II
PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I
interphase (DNA replication before meiosis I)
no interphase (no DNA replication before
meiosis II)
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The Duplicated Chromosome
centromere
Sister Chromatids
One chromosome in the duplicated state
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Chromosome Fate in Meiosis
Sister Chromatids Separate
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Meiosis I
spindle equator
one pair of homologous chromosomes
newly forming microtubules
Anaphase I
Metaphase I
Prophase I
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Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
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Key to Genetic Variation

• There are key events that take place in Meiosis I
  that play a major role in the genetic variation
  among the offspring of sexual reproducers.
• 1. Crossing over in Prophase I
• 2. Random Alignment of homologous chromosomes in
  Metaphase I.

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Crossing Over In Prophase I
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Metaphase I Alignments
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Sperm Formation
primary spermatocyte (diploid)
spermato-gonium (diploid )
sperm (mature, haploid male gametes)
secondary spermatocytes (haploid)
spermatids (haploid)
Meiosis I, Cytoplasmic Division
Meiosis II, Cytoplasmic Division
Growth
cell differentiation, sperm formation
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Egg Formation
first polar body (haploid)
three polar bodies (haploid)
primary oocyte (diploid)
oogonium (diploid)
secondary oocyte (haploid)
ovum (haploid)
Meiosis I, Cytoplasmic Division
Meiosis II, Cytoplasmic Division
Growth