Molecular & Cell Biology

S. Rahgozar,PhD

University of Isfahan

Faculty of Science

3. Cell Cycle

3. 3. Mitosis regulation, Meiosis and Fertilization

1392-93

Cytokinesis

Cell wall formation in plant cells

Cell wall formation in plant cells

New cell wall formation

Meiosis

Sister

chromatids Prophase I

Metaphase I

Prophase I: Stages

Synaptonemal complex at pachytene

in a lily flower Partially synapsed bivalents at zygotene Fully synapsed bivalents in fungus Sordaria

Prophase I: Stages

Prophase I: Pairing of duplicated homologs

A synaptonemal

complex

Transverse filaments

Metaphase I to telophase II

Shugoshins inhibit separase

dependent cleavage of cohesin

Chromosome segragation

in meiosis

Meiosis of vertebrate oocytes

They remain until fertilization

Fertilization

The metaphase to anaphase transition is triggered by

activation of the APC/C, resulting from Ca++ dependent

phosphorylation and degradation of the APC/C inhibitor

Emi/Erp1 for maintaining metaphase II arrest

Comparison of Meiosis in Female and male

Oocytes begin meiosis in the fetal ovary but arrest after diplotene.

Meiosis I is completed only at ovulation.

Meiosis II is completed only after the egg is fertilized.

Completions of meiosis is equivalent to the end of maturity.

Meiosis begins in spermatocytes in the testes at puberty and then

goes on continuously.

completion of meiosis takes 24 days.

A sperm that has completed meiosis has only just begun its

differentiation.