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Oogenesis

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from the equivalent procedure of spermatogenesis in males. First, meiotic divisions during oogenesis are asymmetric, meaning that a large oocyte (containing most of the cytoplasm) and minor polar body are produced as a result of meiosis I, and again following meiosis II. Since only oocytes will go on to form embryos if fertilized, this unequal...

Oogenesis

Oogenesis

Oogenesis, the process of developing egg cells (female gametes), occurs within the ovaries and is fundamental to female fertility. This sequence begins during fetal development when diploid oogonia in the developing ovaries undergo mitotic divisions to produce primary oocytes. By birth, these primary oocytes enter prophase I of meiosis but become arrested in this stage, remaining suspended until puberty.
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Meiosis vs. Mitosis

Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
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Meiosis II

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila,...

Folliculogenesis

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Folliculogenesis is the development of ovarian follicles, the specialized structures within the ovarian cortex where oogenesis, or egg development, occurs. This process is essential for female reproductive health and begins during fetal development when primordial follicles are formed. Each primordial follicle comprises a primary oocyte in the center, surrounded by a single layer of squamous pre-granulosa cells. These follicles remain dormant in late prophase I of meiosis until triggered by...

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A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...

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Related Experiment Video

Updated: Feb 28, 2026

Human Egg Maturity Assessment and Its Clinical Application

Human Egg Maturity Assessment and Its Clinical Application

Published on: August 19, 2019

Mitochondria aggregation patterns during human oocyte maturation.

Adrian Ellenbogen¹, Gal Bachar^1,2, Paz Gili¹

¹Rappaport School of Medicine, Technion - Israeli Institute of Technology, Haifa, Israel.

Human Fertility (Cambridge, England)

|February 27, 2026

Summary

Mitochondrial distribution in human oocytes shifts from peripheral in immature stages to a diffuse pattern in mature oocytes. This dynamic change is linked to improved cytoplasmic maturation and developmental competence.

Keywords:

Mitochondria distribution maturation oocyte cytoplasm

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Area of Science:

Reproductive Biology
Cell Biology
Developmental Biology

Background:

Mitochondrial distribution is crucial for oocyte maturation and developmental potential.
Abnormal mitochondrial localization correlates with impaired cytoplasmic maturation and reduced competence.

Purpose of the Study:

To characterize mitochondrial distribution dynamics in human oocytes during maturation.
To correlate mitochondrial patterns with oocyte developmental stages.

Main Methods:

Analysis of discarded human oocytes from intracytoplascial sperm injection (ICSI) cycles.
Microscopic examination of mitochondrial concentration and distribution patterns.
Comparison of mitochondrial distribution across germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) stages.

Main Results:

Immature GV oocytes predominantly showed peripheral mitochondrial distribution (53%).
Mature MII oocytes exhibited a homogeneously diffuse pattern (61%).
Mitochondrial density significantly increased from GV to MII stages (p=0.003), as did cytoplasmic occupancy (p<0.001).

Conclusions:

Human oocyte maturation involves increased mitochondrial density and cytoplasmic occupancy.
Mitochondrial distribution shifts from peripheral in immature oocytes to diffuse in mature oocytes.
This dynamic mitochondrial patterning is vital for successful cytoplasmic maturation and subsequent embryonic development.