Cell Division

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Cell Division

• SOL BIO 6 a-c

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Meiosis

• Meiosis occurs in sexual reproduction when a
  diploid germ cell produces four haploid daughter
  cells that can mature to become gametes (sperm or
  egg).

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Meiosis

• Goal reduce genetic material by half
• Why? n (mom) n (dad) 2n (offspring)

Just right!
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Meiosis cell division in two parts
Sister chromatids separate
Chromatids separate
(equational division)
2n
n
n
Result one copy of each chromosome in a gamete.
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Meiosis I the reduction division
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Prophase I
Early prophase Chromatids pair. Crossing over
occurs.
Late prophase Chromosomes condense. Spindle
forms. Nuclear envelope fragments.
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Metaphase I
Chromatid pairs align along the equator of the
cell.
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Anaphase I
Chromosomes separate and move to opposite
poles. Sister chromatids remain Attached at
their centromeres.
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Telophase I
Nuclear envelopes reassemble. Spindle
disappears. Cytokinesis divides cell into two.
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Meiosis II
Gene X
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Meiosis II the equational division
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Prophase II
Nuclear envelope fragments. Spindle forms.
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Metaphase II
Chromosomes align along equator of cell.
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Anaphase II
Sister chromatids separate and move to opposite
poles.
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Telophase II
Nuclear envelope assembles. Chromosomes
unravel. Spindle disappears. Cytokinesis
divides cell into two.
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Results of meiosis

• Four haploid cells
• One copy of each chromosome

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Putting It All Together - Fertilization
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What Meiosis is About
Meiosis allows the creation of unique
individuals through sexual reproduction.
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Mitosis Meiosis
Number of divisions 1 2
Number of daughter cells 2 4
Genetically identical? Yes No
Chromosome Same as parent Half of parent
Where Somatic cells Sex cells
When Throughout life At sexual maturity
Role Growth and repair Sexual reproduction
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MITOSIS MEIOSIS
Occurs in somatic (body) cells Occurs only in gonads (sex organs ovary/testes)
Produces cells for repair, maintenance, growth, asexual reproduction Only produces gametes (sex cells egg/sperm)
Results in identical diploid (2n) daughter cells Reduction division results in haploid (n) cells