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Meiosis - PowerPoint PPT Presentation


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Meiosis. First nuclear division 46 X’s split into 2 nuclei with 23 X’s (one of each kind of chromosome) Second nuclear division 23 X’s split into 2 nuclei with 23 single copy chromosomes Cytokinesis follows both divisions, but interphase only follows second division. Meiosis (Prophase I).

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meiosis
Meiosis
  • First nuclear division
    • 46 X’s split into 2 nuclei with 23 X’s (one of each kind of chromosome)
  • Second nuclear division
    • 23 X’s split into 2 nuclei with 23 single copy chromosomes
  • Cytokinesis follows both divisions, but interphase only follows second division.
meiosis prophase i
Meiosis (Prophase I)
  • Process: synapsis
  • Two pairs of homologous = tetrad
  • Trading chromosome pieces is crossing over.
  • The X formed by “legs” of the chromsomes overlapping is called a chiasma
where
Where
  • Mitosis: Any cell not in G0 phase, except in the gonads (ovaries and testes)
  • Meiosis: In the gonads, the germ cells give rise to the gametes (egg and sperm)
slide5
When
  • Mitosis: throughout life in some cells, but cell division stops in nerve cells and muscle cells early in life (2-3 years old).
  • Meiosis:
    • Females: Begins before two years old, then starts again during puberty with one egg made each month. Menopause is when eggs are no longer formed.
    • Males: Happens throughout life from puberty to death.
result
Result
  • Mitosis: 2 Diploid cells with 46 single copy chromosomes.
  • Meiosis: 4 haploid cells with 23 single copy chromosomes (one of each kind)
    • Males: All four are viable cells (sperm)
    • Females: Of the four cells created, only one will become an egg and the other three becoming polar bodies with little cytoplasm, yet having the full 23 chromosomes.