Cell Reproduction

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Cell Reproduction
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Chromosome Structure Review

• Except for the gametes, humans have 46
  chromosomes (23 pairs) in the nucleus of every
  cell.
• Chromosomes are long strands of DNA (genetic
  code).
• When chromosomes are uncoiled, they are called
  chromatin.
• When chromosomes are coiled, they look like a x.

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Chromosome Structure Review
Chromatids- Each half of a chromosome Each
chromatid is a double helix (twisted ladder)
Centromere- holds 2 chromatids together
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Cells with different numbers of chromosomes

• Diploid (somatic cell) A cell consisting of
  homologous chromosomes . In humans, this cell has
  46 chromosomes. One chromosome of a pair came
  from the mother and one from the father. All
  cells in the human body are diploid except sex
  cells.
• Haploid (gamete) A cell that does not contain
  chromosome pairs. The sperm and egg are haploid
  and, in humans, have 23 chromosomes.

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Chromosome Shorthand

• n of unique chromosomes (haploid)
• 2n of chromosomes in pairs (diploid)

n4 Haploid cell
2n8 Diploid cell
XX
X
XX
X
xx
x
Homologous Pair
xx
x
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Cell Cycle- Series of events for cells

• Interphase is the time between cell division.
  This is when the cell grows and replication
  occurs (chromatids are copied). During
  interphase, DNA is uncoiled (chromatin).
• Mitosis/Meiosis is the division of the cells
  nucleus (chromosomes).
• Cytokinesis is division of the cells cytoplasm
  and membrane. This is when the cell physically
  splits in half.

 
 
Cytokinesis
Interphase
Mitosis or Meiosis
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MITOSIS

• Mitosis results in new cells with genetic
  material identical to that of the original cell.
  This process is the reason for human growth.
• Mitosis occurs in all cells of the body except
  the sex cells (egg and sperm cells). Sex cells
  undergo a different process called meiosis.
• Mitosis has 4 phases Prophase, Metaphase,
  Anaphase and Telophase.

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PROPHASE

• DNA supercoils (goes from chromatin to
  chromosomes)
• Nuclear membrane breaks down
• Nucleolus breaks down
• Mitotic spindle forms from the centrosomes
  (containing 2 centrioles)

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METAPHASE

• Chromosomes line up in single file at the center
  of the cell.
• The chromosomes (at the centromere) are held in
  place by the mitotic spindle.

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ANAPHASE

• The chromatids of each chromosome separate and
  move toward opposite poles of the cell.
• The spindle pulls the chromatids apart at their
  centromere.

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TELOPHASE (opposite of Prophase)

• Mitotic spindle breaks down
• Chromosomes uncoil (become chromatin)
• Nuclear envelopes reform
• Nucleolus reappears within each envelope

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CYTOKINESIS

• Cytokinesis occurs differently in animal and
  plant cells.
• In animal cells, the cell membrane pinches in
  until it eventually splits the cell into two.
• This pinching in is called a cleavage furrow.

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CYTOKINESIS

• In plant cells, cytokinesis occurs when a cell
  plate forms and splits the cell into two.
• The cell plate starts to form in the center and
  works its way outward until it reaches the cell
  wall.

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Mitosis and Cytokiinesis Practice

• Each student kit needs
• one 8 foot orange string cut in ½
• One 5 foot black string cut in ½
• 1 clear spoon and fork
• 1 white spoon and fork
• 2 pom-poms
• 2 paper clips
• 8 coffee stirrers

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What is the cell cycle phase? (IPMATC)
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What is the cell cycle phase? (IPMATC)
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What is the cell cycle phase? (IPMATC)
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What is the cell cycle phase? (IPMATC)
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What is the cell cycle phase? (IPMATC)
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What is the cell cycle phase? (IPMATC)
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Meiosis

• A type of cell division in which the chromosome
  is reduced by half to produce haploid cells.
• This produces gametes (sex cells).
• Meiosis has the same phases as mitosis however,
  it goes through 2 rounds of these phases. The
  phases of meiosis are Prophase I/II, Metaphase
  I/II, Anaphase I/II and Telophase I/II.

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PROPHASE I

• Nuclear membrane breaks down
• Nucleolus breaks down
• Mitotic spindle forms from the centrosomes
• Chromatin coils to become chromosomes
• Homologous chromosomes position themselves next
  to each other- This is called synapsis.
• Crossing over occurs- This is when homologous
  chromosomes swap pieces of DNA with each other.

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METAPHASE I

• Homologous pairs line up along the midline of the
  cell.

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ANAPHASE I

• Homologous chromosomes move away from each other
  toward opposite poles of the cell.

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TELOPHASE I

• Nuclear membrane forms around each set of
  chromosomes
• Spindle breaks down
• Chromosomes do not uncoil and nucleoluses do not
  form because there is a second round of nuclear
  division.
• This is followed by Cytokinesis I which produces
  2 haploid cells.

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PROPHASE II

• Nuclear membrane breaks down
• Spindle forms

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METAPHASE II

• Chromosomes line up in single file along the
  midline of the cell.

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ANAPHASE II

• Chromatids of chromosomes separate and move to
  opposite poles of the cell.

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TELOPHASE II

• Chromosomes uncoil to become chromatin.
• Nuclear membranes form around each set of
  chromosomes
• Nucleoluses form in each nuclear membrane.
• Spindle breaks down.
• This is followed by Cytokinesis II which produces
  4 haploid cells.

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Differences between mitosis and meiosis

• Mitosis
• Metaphase- chromosomes are in single file
• 2 product cells (diploid)
• Somatic cells (non-sex) produced
• 4 phases (PMAT)

• Meiosis
• Metaphase I chromosomes are aligned as pairs
• 4 product cells (haploid)
• Sex cells (gametes) produced
• Synapsis and crossing over occurs during Prophase
  I
• 8 phases (PMAT 1 and 2)

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What if meiosis yields sex cells with lt or gt23
chromosomes?

• Down Syndrome
• Turner Syndrome
• Klinefelter Syndrome