File:Oogenesis and meiosis cartoon.jpg

Oogenesis and Meiosis

Meiosis

Female meiosis can be divided into 3 temporally distinct phases.

1. Prophase - after DNA replication, homologous chromosomes (shown in red and blue) undergo pairing, synapsis and recombination, and arrest at the diplotene (dictyate) stage.
2. Dictyate arrest - oocytes remain in meiotic arrest until the female reaches maturity and the oocyte has completed an extensive period of growth following follicle formation.
3. Divisions - luteinizing hormone (LH) surge that triggers ovulation also causes resumption and completion of the first meiotic division in the periovulatory oocyte. The ovulated egg is arrested at second meiotic metaphase, and anaphase onset and completion of meiosis II only occur if the egg is fertilized.

Oogenesis

The process of making an egg is complex and involves 4 distinct developmental phases.

1. Commitment to meiosis and meiotic initiation, which occurs at 8–10 weeks of gestation in humans.
2. Follicle formation, which occurs during the second trimester in humans.
3. Oocyte growth, which occurs in the sexually mature female under the control of paracrine and endocrine signals. Oocyte growth is thought to take approximately 85 days in humans and typically culminates in the ovulation of a single egg.
4. Fertilization of the ovulated egg results in the completion of the second meiotic division.

Links: Oocyte Development | Meiosis | Ovary Development

Reference

Nagaoka SI, Hassold TJ & Hunt PA. (2012). Human aneuploidy: mechanisms and new insights into an age-old problem. Nat. Rev. Genet. , 13, 493-504. PMID: 22705668 DOI.

Copyright

Reprinted by permission from Macmillan Publishers Ltd: Nature Reviews Genetics (doi: 10.1038/nrg3245), copyright (2012)

Figure 1. Original figure resized and relabelled with text and PubMed ID. Above text from figure legend.

Cite this page: Hill, M.A. (2024, April 27) Embryology Oogenesis and meiosis cartoon.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Oogenesis_and_meiosis_cartoon.jpg

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G