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!