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MEIOSIS

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MEIOSIS Why Meiosis increases Genetic Variation Assortment of Chromosomes Genetic Recombination (Crossing Over) Assortment of Chromosomes Crossing Over Crossing Over ... – PowerPoint PPT presentation

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Title: MEIOSIS


1
MEIOSIS
2
Review
  • Homologous Chromosomes
  • matching pair of chromosomes, one inherited from
    each parent

3
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

4
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?

4
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32
Diploid
5
II. Meiosis
  • Definition
  • cell division to produce egg (ovule) or sperm
    (pollen)

6
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

7
  • 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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23
46
  • 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.

11
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

31
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)

35
Assortment of Chromosomes
36
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
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