Meiosis

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Meiosis
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Meiosis

• Haploid cells
• Diploid cells
• Somatic cells
• Gametes
• Role of Meiosis
• To produce haploid gametes from diploid germ
  cells.
• Occurs only in the gonads

• Plays an important role in creating genetic
  variability through the processes of
• Segregation
• Independent assortment
• Crossing over

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Meiosis

• Interphase
• S phasereplication
• Cell is now diploid with all chromosomes being
  mitotic
• Meiosis Ireductive division
• Creates 2 haploid cells with mitotic chromsomes
• Consists of several stages

• Prophase ILike prophase in mitosis.
• Synapsishomologous chromosomes attach to form
  tetrads.
• Crossing over occurs.
• Reshuffling of genes. Genetic recombination.
  Important for creating variability.

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Meiosis

• Metaphase Itetrads are aligned in such a way
  that the homologous chromosomes are situated
  across from each other.
• Independent Assortmentmaternal and paternal
  chromosomes are line up on the opposite sides of
  the metaphase plate in a random fashion. When
  these homologues split during anaphase I. The
  new nuclei consist of a mixture of maternal and
  paternal

• Importance for genetic variability.
• Telophase ISimilar to telophase in mitosis.
• Cytokinesis
• Interphase II or interkinesis II.
• Now have 2 haploid cells with mitotic
  chromosomes.
• Very brief. No DNA replication

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Meiosis II

• Almost the same as Mitosis.
• 2 cells are formed from each of the cells from
  Meiosis I.
• These cells are haploid and have chromosomes
  formed by only one chromatid.
• These cells develop into gametes

• Prophase II
• Metaphase II
• Anaphase II
• Telophase II
• Cytokinesis
• Results in 4 haploid cells that will eventually
  form gametes

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Gametogenesis

• In males
• spermatogenesis
• 1 diploid germ cell goes through meiosis to form
  4 haploid cells. These develop in the testes to
  form sperm.

• In females
• Oogenesis
• 1 diploid germ cell split unequally into 4
  haploid cells.
• The large cell develops into an egg.
• The small cells are know as polar bodies and
  usually die.
• Why does this unequal division occur?

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