Lab 9 Meiosis Prelab 9 and the Lab

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 1 st 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 copy DIPLOID = 2 copies

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

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!