Meiosis

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Meiosis

• HS Biology

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Sexual Reproduction

• Two sex cells, usually an egg and a sperm, come
  together.

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Fertilization

• The joining of an egg and a sperm, generally from
  two different organisms of the same species.
• Sperm from male reproductive organs
• Eggs formed in the female reproductive organs

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More on fertilization

• A cell that forms from fertilization is a zygote.
• Following fertilization, mitosis begins and a new
  organism develops.

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Division of sex cells

• Body cells are diploid, because they have 23
  pairs of similar chromosomes (46 total)
• Sex cells are haploid, because they have 23
  chromosomes.

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Meiosis

• A process that produces haploid sex cells
• In meiosis I, the nucleus divides and produces
  two new cells with one chromosome each.

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Meiosis II

• The nuclei divide and the chromatids separate,
  producing four cells with half the number of
  chromosomes of the original nucleus.

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Additional Notes

• There are a few special things that happen in
  meiosis.
• In Prophase I, the chromosomes undergo a process
  called SYNAPSIS
• Each chromosome pairs up with its homologue (the
  one that is the same size and shape)

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P Paternal for your dads chromosomes M
Maternal for your mothers chromosomes
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Crossing Over

• During synapsis, one chromatid of each homologous
  chromosome crosses over a chromatid of the
  opposite homologous chromosome at one or more
  points
• As the chromosomes twist around each other,
  fragments may break off and be exchanged with the
  homologous pair.

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Anaphase I

• The two chromatids making up each chromosome do
  not separate.
• The chromosomes comprising a homologous pair
  become pulled to opposite ends of the cell
• Each daughter cell ends up with only one
  chromosome of each pair, although each chromosome
  still consists of two chromatids.

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