Cell division to produce gametes

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MEIOSIS

• Cell division to produce gametes

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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis
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Meiosis

• Just as in mitosis, meiosis begins with a diploid
  cell. Diploid cells have two copies of every
  chromosome one from the organisms father and
  one from its mother.

This cell has two unique chromosomes. The
diploid (2n) number is 4. The haploid (n) number
is 2.
Maternal chromosome 1
Maternal chromosome 2
Paternal chromosome 1
Paternal chromosome 2
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Meiosis

• During interphase, all of the DNA is copied
  through a process called DNA replication. Each
  chromosome now contains two identical sister
  chromatids, connected at a centromere.

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Meiosis

• During prophase, the strands of DNA are wrapped
  around proteins called histones to form these
  condensed structures called chromosomes.
• So far, this has been the exact same process as
  mitosis.

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Meiosis

• During metaphase I, homologous chromosomes are
  pulled to the center of the cell. The nuclear
  envelope has degraded.

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Meiosis

• During anaphase I, homologous chromosomes are
  separated from each other, but sister chromatids
  remain attached to each other.

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Meiosis

• In telophase I, other cellular components are
  separated and the cell divides in half. Now each
  daughter cell contains one of each chromosome,
  but each contains two (nearly) identical copies.

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Meiosis

• Now the two daughter cells immediately enter
  another phase of division (meiosis II). After the
  nuclei break apart, fibers attach to the sister
  chromatids.

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Meiosis

• In metaphase II, the chromosomes are lined up
  with their centromeres in the center of the cell.
  The sister chromatids are still attached to each
  other.

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Meiosis

• In anaphase II, the sister chromatids are pulled
  apart from each other.

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Meiosis

• In telophase II, a nuclear envelope forms around
  the chromosomes, the cytoplasm divides once more
  (cytokinesis) to form four daughter cells, and
  the gamete is ready to go.

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SUMMARY

• Meiosis is the process of cell division that
  produces haploid sex cells (gametes).
• Each diploid cell that undergoes meiosis produces
  four haploid cells.
• Two processes increase genetic diversity in
  meiosis crossing over (during metaphase I) and
  independent assortment of chromosomes (during
  anaphase I and anaphase II).