Do-Now: Review from Mitosis

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Do-Now Review from Mitosis

• A human body cell has 46 chromosomes. In a human
  body cell, mitosis produces
• A) two cells with 46 chromosomes in each.
• B) two cells with 23 chromosomes in each.
• C) four cells with 23 chromosomes in each.
• D) four cells with 46 chromosomes in each.

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Do-Now Review from Mitosis

• A human body cell has 46 chromosomes. In a human
  body cell, mitosis produces
• A) two cells with 46 chromosomes in each.
• B) two cells with 23 chromosomes in each.
• C) four cells with 23 chromosomes in each.
• D) four cells with 46 chromosomes in each.

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Mitosis Review

• In mitosis, a parent body cell divides to make
  two daughter body cells
• New daughter cells are diploidhave two sets of
  chromosomes (46 total in humans)
• Example one blood cell divides to make two blood
  cells

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Mitosis Review

• Only DIPLOID cells are made in mitosis

Diploid Haploid
Sets of Chromosomes 2 1
Total of chromosomes in humans 46 23
Type of Cell Body cell (ex, blood cell, bone cell) Sex cell (sperm or egg cell)
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Meiosis- A New Type of Division

• During meiosis, new SEX CELLS (eggs and sperm)
  are created.
• 2) Eggs and sperm are haploid, meaning they have
  one set of chromosomes (23 total).

Why might it be a problem for sex cells to be
diploid ?
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Meiosis

• A process where the nucleus divides that splits
  the original chromosomes into haploid daughter
  cells
• Human Body Cell 46
• Egg or Sperm Cell 23
• Why?... so that chromosome number wont be
  doubled during fertilization
• Key Point Meiosis makes fertilization
  possible!!!

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Types of Reproduction

• Asexual makes offspring (children) that are
  identical to the parent (ex binary fission in
  bacteria or budding in sponges)
• 2. Sexual makes offspring that are different
  from the parent, meiosis happens and then sperm
  and egg join

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Stages

• Before meiosis begins Interphase (G1, S, G2)
• What happens during each part of interphase? Is
  this considered part of cell division?
• During Meiosis
• -Meiosis I
• -Meisis II

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Remember the Cell Cycle?
Meiosis uses the same cycle as mitosis, except
meiosis happens in 2 parts. Interphase must
still happen so the cell can grow, copy its DNA,
and prepare for division.
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Meiosis I

• Chromosome number gets cut in half
• (1 diploid cell ? 2 haploid cells)
• 4 parts
• 1) Prophase I
• 2) Metaphase I
• 3) Anaphase I
• 4) Telophase I

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Prophase I

• Similarities to Mitosis
• DNA coils into chromosomes
• Spindle fibers are made
• Nuclear Membrane breaks down

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Prophase I

• Differences from Mitosis
• Homologous chromosomes pair up
• Homologous chromosomes pairs of chromosomes (1
  from mother and 1 from father) that have the same
  genes (ex gene for eye color)

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Prophase I Crossing Over

• Crossing over homologous chromosomes trade
  genes
• Results in Genetic Recombination
• Tetrad the pair of chromosomes

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Why does crossing over take place?

• Trades genes so that offspring look different
  from either parent and from their siblings.

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Prophase I

• Label
• Homologous Chromosomes
• Nuclear Membrane
• Spindle
• Crossing Over

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Metaphase I

• Tetrads line up in the middle of the cell
• Spindle fibers attach to the chromosomes
• Label Homologous Chromosomes, Centromere,
  Spindle, Metaphase Plate

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Anaphase I

• Homologous Chromosomes move to opposite ends of
  the cell
• Label Homologous chromosomes, spindle

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Telophase I and Cytokinesis

• Chromosomes reach opposite ends
• Cytoplasm divides
• End Result 2 daughter cells with half the
  original chromosome number
• Label Nuclear membrane, centrioles, chromosomes

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Meiosis II

• DNA is NOT copied again
• Chromatids (identical copies of DNA) separate
  like they do during mitosis
• 4 Stages
• 1) Prophase II
• 2) Metaphase II
• 3) Anaphase II
• 4) Telophase II and Cytokinesis

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Meiosis II

• End Result of Meiosis 4 haploid daughter cells

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Prophase II

• Nuclear membrane breaks down
• Spindle is made
• Label Nuclear membrane, spindle, chromosomes

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Metaphase II

• Spindle fibers move chromosomes to the center of
  the cell
• Label Chromosomes, Chromatids, Centromere,
  Spindle, Metaphase Plate

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Anaphase II

• Chromatids of each chromosome separate at the
  centromere and move toward opposite ends of the
  cell
• Label New Chromosomes, Spindle

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Telophase II and Cytokinesis

• Spindle breaks down
• Chromosomes uncoil Nuclear envelopes form
• Cytoplasm divides
• Label Nuclear Membrane, Centrioles, Uncoiling
  Chromosomes (chromatin)

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Main Goal Making Sex Cells!

• Gametes haploid reproductive cells made during
  meiosis (ex sperm and egg)
• Sex cells are made in the testes and ovaries in
  humans

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Spermatogenesis

• The process of making sperm cells
• Diploid cell divides by meiosis to form four
  haploid sperm cells

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Spermatogenesis
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Oogenesis

• The process of making egg cells
• A diploid cell divides by meiosis to make ONE
  mature egg cell
• Other three haploid cells polar bodies

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Oogenesis

• Egg gets all the cytoplasm and organelles, polar
  bodies are tiny little structures with DNA only
• Polar bodies break down and die ?

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Warm Up

1. What does it mean to be a diploid cell?
2. How does meiosis make fertilization possible?
3. What are three ways in which asexual reproduction
   is different from sexual reproduction?
4. Is Interphase considered part of cell division?
5. How does crossing over contribute to genetic
   variability?
6. How is the end result of meiosis different from
   the end result of mitosis?
7. How is the one egg cell different from the three
   polar bodies?
8. What is the main difference between
   spermatogenesis and oogenesis?
9. How is Prophase 1 of meiosis and Prophase of
   mitosis different?
10. Which part of meiosis (meiosis 1 or meiosis 2) is
    most like mitosis?

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• Meiosis Poster 8 Section, Label Phases, Draw
  Diagrams, Describe what is Going on at each
  phase, Label. Use COLOR. Follow Chromosomes.
• Prophase 1 Label Homologous Chromosomes,
  Centrioles, Nuclear Membrane, Sister Chromatids,
  Spindle Fibers, Tetrad, Crossing Over
• Metaphase 1 Label Homologous Chromosomes,
  Centrioles, Centromere,
• Spindle
  Fibers, Metaphase Plate, Sister Chromatids
• Anaphase 1 Label Homologous Chromosomes,
  Centrioles, Sister
• Chromatids,
  Spindle Fibers
• Telophase 1 Label Nuclear membrane, Centrioles,
  Spindle Fibers, Homologous
• Chromosomes,
  Sister Chromatids
• Prophase 2 Label Nuclear membrane, Spindle
  Fibers, Centriole, Homologous
• Chromosomes,
  Sister Chromatids
• Metaphase 2 Label Homologous Chromosomes,
  Sister Chromatids,
• Centromere,
  Spindle Fibers, Centrioles, Metaphase Plate
• Anaphase 2 Label Nuclear Membrane, Centrioles,
  Sister Chromatids,
• Spindle
  Fibers
• Telophase 2 Label Nuclear Membrane, Centrioles,
  Uncoiling Sister Chromatids
• (chromatin),
  Spindle Fibers
• Dont Forget to Label Diploid and Haploid

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• On a separate sheet of paper
• compare/contrast Mitosis and Meiosis
• (I can come up with at least 15. . . . How about
  you?)
• DUE Wednesday!! Have a
• WONDERFUL Break ?