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 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!