MEIOSIS

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MEIOSIS
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Review

• Homologous Chromosomes
• matching pair of chromosomes, one inherited from
  each parent

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Review

• Somatic body cells, non sex cells, they are
  diploid
• Diploid or 2N having two sets of chromosomes
• Haploid or N having one set of chromosomes

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Diploid vs. Haploid Exercises

• Drosophilia have a diploid number of 8. What is
  the haploid?
• Onions have a haploid number of 8. What is the
  2N?
• A horses 2N is 64. What is the 1N?
• A body cell of an alligator has 32 chromosomes.
  Is this the diploid or haploid number?

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Diploid
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II. Meiosis

• Definition
• cell division to produce egg (ovule) or sperm
  (pollen)

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Karyotypes

• Display of chromosomes lined up in homologous
  pairs
• Half inherited from male Half from female

• Used for viewing , size, shape, and banding
• patterns of chromosomes

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• Autosomes 1-22
• Chromosomes that are not sex chromosomes
• Sex chromosomes 23
• Mammal females XX
• Mammal males Xy

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Moms Egg 23 chromosomes
Dads Sperm 23 chromosomes
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• Fertilization
• when haploid sperm and egg
• meet, combining N chromosomes
• with N chromosomes
• 2N zygote

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• Zygote fertilized egg, 2N

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General Process of Meiosis

• MEIOSIS I (PMAT I C)
• - Prophase I homologous chromosomes meet up
  
• and form tetrads. Crossing over occurs.

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Process of Meiosis Con.t

• - Metaphase I homologous chromosomes line
  up
• along the equator the assortment among
• homologs is random
• - Anaphase I and Telophase I occur as usual
• - Cytokinesis splits cell in half.
• - Begins with one 2N gametocyte
• - Ends with two 1N cells

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INDEPENDENT ASSORTMENT
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CELL THEN GOES THROUGH INTERKINESIS- NO MORE
DOUBLING OF CHROMOSOMES!!
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General Process of Meiosis

• MEIOSIS II (PMAT II C)
• - Starts with 2 haploid cells
• - Prophase, Metaphase, Anaphase, Telophase II
• and Cytokinesis serve to separate the
  sister
• chromatids
• - Ending Cells 4 cells, each with haploid
• chromosomes

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Another Animation of Overall Meiosis
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Oogenesis Production of Egg

• Female meiosis in the ovaries
• Resulting cells
• 1 egg, 3 polar bodies
• Haploid

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SpermatogenesisProduction of Sperm

• Male meiosis in testes
• Resulting cells
• 4 haploid sperm cells

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Comparison between Spermatogenesis and Oogenesis
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What if Meiosis Did Not Use Haploid Cells?

• Every generation would inherit twice as many
• chromosomes
• Sperm (23) Egg (23) 46 chromosomes
• Sperm (46) Egg (46) 92 chromosomes
• Sperm (92) Egg (92) 184 chromosomes

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Why Meiosis increases Genetic Variation

• Assortment of Chromosomes

• Genetic Recombination (Crossing Over)

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Assortment of Chromosomes
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Crossing Over
Crossing Over can produce a single chromosome
that contains a NEQW Combination of genetic
information from different parents --- this is
GENETIC RECOMBINATION.
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• Mitosis
• Cell division
• 46 chromo?2 cells,
• 46 chromo. Each
• Keeps chromo. same
• Found in body cells
• Most common
• No genetic variation

• Meiosis
• Cell division
• 46 chromo? 4 cells,
• 23 chromo each
• Chromo. cut in half
• Found in sex/germ cells ONLY
• Least common
• Most genetic variation

ANIMATION OF COMPARISON
ANIMATION 2 OF COMPARISON