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Meiosis: The Process. Biology 12. Cartoon of the day:. Context: . Meiosis allows for the formation of sperm and egg cells. Overview:. Interphase Meiosis I Prophase I Metaphase I Anaphase I Telophase I (and cytokinesis) Meiosis II Prophase II Metaphase II Anaphase II

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Presentation Transcript
context
Context:
  • Meiosis allows

for the formation

of sperm and

egg cells

overview
Overview:
  • Interphase
  • Meiosis I
      • Prophase I
      • Metaphase I
      • Anaphase I
      • Telophase I (and cytokinesis)
  • Meiosis II
      • Prophase II
      • Metaphase II
      • Anaphase II
      • Telophase II (and cytokinesis)
meiosis i interphase
Meiosis I: Interphase
  • The chromatin begins to condense into chromosomes, which duplicate
  • Identical to interphase in mitosis

Chromosome duplication

meiosis i prophase i
Meiosis I: Prophase I
  • In meiosis (unlike mitosis), the process called synapsis occurs.
  • Tetrads of homologous chromosome form
  • There may be an exchange of genetic material, called crossing over
crossing over synapsis
Crossing over (synapsis):
  • Non-sister chromatids of homologous chromosomes interchange genes
  • The pairing (formation of the tetrad) allows crossing over to take place and this enables genetic variations in the daughter cells.
meiosis i metaphase i
Tetrads line up at the equator

Alignment is random so that chromosomes from one will be mixed with the other parent when they move apart

Meiosis I: Metaphase I
meiosis i anaphase i
One homologous chromosome of each pair is pulled to each end of the cell.

**Remember in mitosis, it was the chromatids that separated, not pairs of chromosomes!

Meiosis I: Anaphase I
meiosis i telophase i and cytokinesis i
The cell begins to divide into two daughter cells.

Each cell produced after cytokinesis has been reduce from diploid to haploid.

Meiosis I: Telophase I (and cytokinesis I)
interphase
Interphase:

Very short

DNA is not replicated before meiosis II

meiosis ii anaphase ii
Centromeres divide in two

Spindle fibres pull sister chromatids towards opposite ends of cell (pole)

Meiosis II: Anaphase II
result
Result:
  • Formation of four cells
    • Are sex cells (egg or sperm)
    • Haploid (carries half the number of chromosomes of somatic cells)
videos
Videos:
  • http://www.youtube.com/watch?v=kVMb4Js99tA
  • http://www.youtube.com/watch?v=iCL6d0OwKt8
to do
To do:
  • Meiosis colouring sheet
  • Read pages 103-107
    • Page 107 # 1, 2, 3, 4, 5, 6
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