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.
Chromosomes
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 copy
DIPLOID = 2 copies
Haploid gametes (n = 23)
Meiosis
n
Egg cell
n
Sperm cell
Meiosis
A Meiosis video in
a nematode. A
little slow
downloading
but only 24 sec.
Fertilization
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
2n
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!