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Meiosis

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Meiosis A double cell division to produce sex cells (sperm and egg) Meiosis The form of cell division by which gametes, with half the number of chromosomes, are ... – PowerPoint PPT presentation

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Title: Meiosis


1
Meiosis
  • A double cell division to produce sex cells
    (sperm and egg)

2
Meiosis
  • The form of cell division by which gametes, with
    half the number of chromosomes, are produced.
  • diploid (2n) ? haploid (1n)
  • Two divisions (meiosis I and meiosis II)

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Meiosis
  • Sex cells divide to produce gametes (sperm or
    egg)
  • Gametes have half the number of chromosomes
  • Occurs in the gonads (testes or ovaries)
  • Male spermatogenesis
  • Female oogenesis
  • Meiosis is similar to mitosis with some
    chromosomal differences

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Interphase I
  • Similar to mitosis interphase
  • Chromosome replicated (S phase)
  • Each duplicated chromosome consist of two
    identical sister chromatids attached at their
    centromeres
  • Centriole pairs also replicate

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Prophase I
  • Chromosomes condense
  • Synapis occurs homologous chromosomes come
    together to form a tetrad
  • Tetrad is four chromatids (sister and nonsister
    chromatids)

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Homologous chromosomes
  • Pair of chromosomes (material and paternal) that
    are similar in shape and size.
  • Homologous pairs (tetrads) carry genes
    controlling the same inherited traits.
  • Each locus (position of the gene) is in the same
    position on the homologous chromosomes.
  • Humans have 23 pairs of homologous chromosomes
  • 22 pairs of autosomes
  • 1 pair of sex chromosomes

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Crossing Over
  • Crossing over (variation) may occur between
    nonsister chromatids at the chismata.
  • Crossing over segments of nonsister chromatids
    break and reattach to the other chromatids
  • Chismata (chiasma) are the sites of crossing
    over.

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Metaphase I
  • Tetrads align on the metaphase plate (middle)

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Anaphase I
  • Homologous chromosomes separate and move towards
    the poles.
  • Sister chromatids remain attached at their
    centromere

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Telophase I
  • Each pole now has sister chromatids that will be
    separated

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21
Meiosis II
  • No interphase II
  • Very short no need for DNA replication
  • Remember Meiosis II is similar to mitosis

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Telophase II
  • Same as telophase in mitosis
  • Nuclei form
  • Cytokinesis will occur at the end
  • The final product should be four haploid daughter
    cells
  • Gametes sperm or egg

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27
Animation Link
  • Mitosis vs. Meiosis
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