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Lab 9b: Meiosis
• Prelab 9 and Informal Lab Report is due.
• Microworlds are due NEXT CLASS!– You should have time to work on it today.– Turn in all 10 Microworlds including the 4 that
have been graded.– You may use mitosis & meiosis slides for this.
Mitosis makes cells, but what about making babies?
• Does Mitosis produce gametes (sex cells: egg and sperm)?
Meiosis
• Resembles 2 rounds of mitosis• 2 cell divisions (meiosis I and meiosis II)• 4 resulting haploid cells
HAPLOID= 1 copyDIPLOID = 2 copies
MeiosisHaploid gametes (n = 23)
Egg cell
Sperm cell
FertilizationMeiosis
Diploidzygote
(2n = 46)
n
Multicellulardiploid adults
(2n = 46)
Mitosis anddevelopment
2n
n
A Meiosis video in a nematode. A little slow downloading but only 24 sec.
A Meiosis video in a nematode. A little slow downloading but only 24 sec.
Meiosis I: Prophase I
• Chromosomes condense• Nuclear membrane degrades• Centrioles (Spindle fibers)
move to opposite poles• Homologous chromosomes
(homologues) pair up• Crossing over occurs
Meiosis I: Metaphase I
• Spindle fibers attach to centromeres
• Paired Homologues line up on equator (metaphase plate)
Meiosis I: Anaphase I
• Homologues separate (each still consists of two sister chromatids)
• Chromosome # halves (counting centromeres)
• Cells destined to be haploid
Meiosis I: Telophase I
• Nuclear membranes reforms
• Cytokinesis follows• Haploid cells as the
homologs split not the sister chromatids
Meiosis II: Prophase II
• Chromosomes condense again
• Nuclear membrane breaks down
• 2 sister chromatids to 1 chromosome
Meiosis II: Metaphase II
• Spindle fibers attach to centromeres
• Chromosomes line up on the metaphase plate
Meiosis II: Anaphase II
• Sister chromatids separate and move to opposite plates
• The microtubules contract, moving the chromatids
Meiosis II: Telophase II
• Nuclear membranes reforms
• Chromosomes unwrap• Cytokinesis follows• 4 haploid cells produced
(at least in males, oogenesis is more complicated)
Ex. 1: Modeling Meiosis
• Use either Play-doh or the Pop Beads to model meiosis
• Make a diploid cell with 3 chromosomes of different sizes.
• Be sure to model all the steps in meiosis• One of the exercises models crossing over• Important, answer the Study Guide Questions at the
end of the lab. It compares mitosis and meiosis.
Rest of Lab
• When finished, your table group needs to walk me through the steps of meiosis w/o using notes or the manual!
• If I pass you, turn in a list of your names.• Work on your Microworlds project, due next
week. (Micoworld slides, pond water, mitosis/meiosis slides available.)
• When you are all done, you are free to go!