BY5.1 Meiosis

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  • involves 2 divisions of the cell
  • in meiosis I - 2 daughter cells are produced with half the number of chromosomes of the parental nucleus
  • in meiosis II - 2 new haploid nuclei divide again in a division identical to mitosis

result: 4 haploid nuceli formed from the parental nuclei


  • occurs when the cell is not dividing
  • DNA doubles
  • new organelles are formed

Meiosis I:

Prophase I:

  • chromosomes split into 2 chromatids
  • centrioles move to the poles of the cell
  • spindles forms
  • chromosomes assocaite into homologous pairs - known as bivalents
  • crossing over occurs at chiasmata
  • nuclear membrane disintegrates
  • nucleolus disappears

Metaphase I:

  • pair of homologous chromosomes line up on the equator of the spindle
  • maternal and paternal chromosomes are arranged randomly
  • random distribution and subsequent independent assortment preoduces new genetic combinations

Anaphase I:

  • chromsomes of each bivalent separates and are pulled to the poles
  • nuclear envelope…


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