Lab 9: Meiosis
Prelab 9 and the Lab report is due.Lab 8 is due by the end of the class. (You may
work on the 1st part in lab today. Make sure you turn it in or it is late.)
Microworlds is due NEXT CLASS – you should have tons of time to work on it today
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 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.
Meiosis I: Prophase I• Chromosomes
condense• Homologous
chromosomes (homologues) pair up
• Crossing over occurs• Nuclear membrane
degrades
Meiosis I: Metaphase I• Spindle fibers attach to
centromeres• Homologues line up on
equator (metaphase plate)
Meiosis I: Anaphase I• Homologues separate
(each still consists of two sister chromatids)
• Chromosome # halves (counting centromeres)
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• This only looks as
shown when viewed from the equator, it looks like a mess when viewed from the poles.
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, we’ll skip the more complicated oogenesis)
Modeling Meiosis with Play-doh
• 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
Rest of Lab
• If needed, finish the protein synthesis part of Lab 8. Turn it in before you go.
• Work on your Microworlds project, it is due next week. (Slides and pond water available.)
• When you are all done, you are free to go!