Mitosis and Meiosis

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Mitosis and Meiosis
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Cell cycle and mitosis

• Mitosis consists of 10-20 of cell cycle,
  depending on cell type
• Interphase refers to remainder of cell cycle
• Three phases G1, S, G2
• Mitosis often referred to as M phase
• DNA is duplicated during S phase in preparation
  for next mitotic division

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Meiosis

• Produces 4 haploid daughter cells through 2
  divisions from parent cell
• Only in germ (reproductive) cells, not in somatic
  (body) cells
• reduction division
• Chromosome number is reduced during first
  division
• Second division maintains chromosome number
• Bivalents are formed during prophase I
• Dissociate during anaphase I to produce dyads
  consisting of two identical DNA strands
  (chromatids) attached at centromere
• Chromatids of dyad dissociate during anaphase II
• Chromosome number is maintained (count
  centromeres)
• Meiosis II is similar to a mitotic division

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Early Prophase I

• 5 phases leptotena, zygotena, pachytena,
  diplotena, diakinesis
• Synapsis occurs
• Homologous chromosomes recognize each other
• Align across entire length to form tetrad (4
  chromatids in synaptonemal complex)
• Crossing over occurs
• Begins in zygotena prior to completion of
  synapsis, continues into pachytena

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Crossing over
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Metaphase I

• Homologous pairs of chromosomes (bivalents) line
  up together at metaphase plate (unlike in
  mitosis)
• Duplicated DNA strands (sister chromatids) DO NOT
  separate during anaphase

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Meiosis I attachment of spindle

• Each pair of sister chromatids attached to only
  one pole
• Different from attachment in mitosis and meiosis
  II

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Anaphase I and Telophase I
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Meiosis II
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Summary meiosis I
Duplicated copies of Chromosome 1
Chromosome 1 (pair in normal cell)
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Summary meiosis I
Duplicated chromosomes separate
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Summary meiosis I
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Summary meiosis II
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Summary meiosis II