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#oogenesis

3 public questions tagged with this topic.

Fertilization in mammals-l

At birth, mammalian oocytes are arrested in:

Mammalian oocytes enter meiosis during embryonic life and become arrested in diplotene of prophase I within primordial follicles, known as dictyate stage with intact germinal vesicle nucleus and homologous chromosomes held by chiasmata. High intra-oocyte cAMP maintained by cumulus-derived signals and phosphodiesterase inhibition sustains arrest by preventing MPF activation. At birth ovaries contain approximately one million follicles dormant in this state lasting until puberty when LH surges trigger meiotic resumption. Arrest permits extensive growth, accumulation of maternal transcripts, organelles essential for early embryogenesis, zygotic reprogramming, developmental competence and embryonic viability.

Ref: Alberts, Molecular Biology of the Cell, Chapter 21: Oocyte arrest in prophase I dictyate stage until LH surge.

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Fertilization in mammals-l

Cells produced as by-products during oogenesis:

Oogenesis features highly asymmetric cytokinesis preserving ooplasmic resources for embryogenesis. During meiosis I and II, division planes are peripheral, extruding diminutive cells called polar bodies containing excess haploid chromatin sets with minimal cytoplasm. First polar body formed after meiosis I may further divide. Polar bodies degenerate without developmental role, allowing preferential retention of mitochondria, mRNAs and nutrients in secondary oocyte and later ovum. This conservative allocation contrasts with symmetric spermatogenesis producing four functional gametes from one spermatocyte efficiently conserving maternal reserves for early embryonic development, genome activation and cleavage support.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Oogenesis and formation of polar bodies during asymmetric meiosis.

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Fertilization in mammals-l

Gametogenesis in mammals primarily occurs through:

Gametogenesis requires combination of mitotic proliferation and meiotic reduction to balance gamete quantity and ploidy. Primordial germ cells and spermatogonial stem cells divide mitotically expanding pool and in males maintaining lifelong production. Subsequent entry into meiosis halves chromosome number via homologous recombination and two sequential divisions, generating genetically diverse haploid spermatids or oocytes. Pure mitosis would retain diploidy incompatible with fertilization restoring diploidy, while meiosis alone without mitotic amplification would insufficiently produce gamete numbers. Dual program ensures both amplification, genetic variability, sustainable fertility across reproductive lifespan and gamete quality.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 19: Gametogenesis – mitosis and meiosis in mammalian germ cell development.

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