Meiosis

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Meiosis
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Mitosis vs. Meiosis
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Mitosis vs. Meiosis

• BOTH INVOLVE CELL DIVSION
• Goal of Mitosis to produce 2 daughter cells that
  are genetically identical to the parent (same
  DNA).
• -Used for growth
• -1 set of division
• -1 diploid cell ? 2 diploid cells

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Mitosis vs. Meiosis

• Goal of Meiosis to produce sperm or eggs, also
  called gametes contains ½ the genetic
  information as the parent.
• -Used for reproduction
• -2 sets of division
• -1 diploid cell ? 4 haploid cells

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Diploid vs. Haploid Cells

• Diploid having 2 sets of chromosomes (2n).
• Ex human body cells have 46 chromosomes
• Haploid having one set of chromosomes, as in a
  sperm or egg (n).
• Ex human egg and sperm cells have 23
  chromosomes.

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Haploid Diploid
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Meiosis

• Meiosis animation
• http//www.youtube.com/watch?vD1_-mQS_FZ0NR1
  

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In Meiosis there are 2 sets of division taking
place.
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Interphase occurs before Meiosis begins.
In Interphase, the chromosomes have not yet
condensed into distinct chromosomes.
http//morgan.rutgers.edu/MorganWebFrames/Level1/P
age7/meiosis1.html
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Interphase
The chromosomes have replicated (made a double),
and prepares for division.
http//morgan.rutgers.edu/MorganWebFrames/Level1/P
age7/meiosis1.html
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Replicated DNA

• DNA is replicated along with organelles and other
  cellular components and the cell prepares for
  division.
• Each half of the duplicated chromosome is called
  a sister chromatid.
• Chromatids are connected to each other by
  centromeres. 

http//www.bioweb.uncc.edu/1110Lab/notes/notes1/la
b6.htm
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Meiosis - Prophase I
The chromosomes are completely condensed. In
meiosis (unlike mitosis), the homologous
chromosomes pair up with one another. Crossing
over occurs, in which homologous chromosomes
exchange genetic material.
http//morgan.rutgers.edu/MorganWebFrames/Level1/P
age7/meiosis1.html
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Meiosis - Metaphase I

• The nuclear membrane has dissolved.
• Homologous pairs line up in the middle of the
  cell.
• Spindle fibers attach to each homologous
  chromosome.

http//morgan.rutgers.edu/MorganWebFrames/Level1/P
age7/meiosis1.html
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Meiosis - Anaphase I

• Spindle fibers shorten.
• The chromosomes move to opposite ends of the
  cell.
• Notice that these are chromosomes, not
  chromatids!!

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Meiosis - Telophase I Cytokinesis

• The cell begins to divide into two daughter
  cells.
• It is important to understand that each daughter
  cell can get any combination of maternal and
  paternal chromosomes, because of crossing over.

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Meiosis - Prophase II

• The nuclear envelope begins to break down.
• The spindle fiber forms.
• Compare the next few steps to Mitosis!

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Meiosis - Metaphase II

• A haploid number of chromosomes line up in the
  middle of the cell.
• Spindle fibers connect to the centromeres.
• Do you remember what haploid means?

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Meiosis - Anaphase II

• The spindle fibers shorten and the sister
  chromatids move to opposite sides of each cell.
• Looks similar to Anaphase in Mitosis.

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Telophase II Cytokinesis

• The chromosomes reach the poles, and the nuclear
  membrane reforms around each nucleus.
• Meiosis results in four gametes, or sex cells
• Each carries half the number of chromosomes of
  regular body cells.

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Is Meiosis I or Meiosis II more similar to
Mitosis?

• Answer Meiosis II (the second division) is more
  similar to Mitosis.