Embryogenesis Question

Jacob_Arulandu
Jacob_Arulandu Posts: 34

MCAT Student

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in Pre-Med Success Community

Hello,

If during oogenesis the 2º oocyte must wait until fertilization to undergo meiosis II then how come the ovum is not diploid. If the sperm has penetrated the zona pellucida and the 2º oocyte and the spermatid cells are both haploid wouldn´t integration of the genetic material mean that the fertilized ovum is diploid?

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  • Ae-Ri
    Ae-Ri Posts: 225

    Moderator

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    Answer ✓

    Hi Jacob

    At birth, the eggs are all halted in meiosis I, so they are all primary oocytes, which are diploid. Menses triggers the completion of meiosis I of the primary oocyte to result in the secondary oocyte, which is haploid. That secondary oocyte then holds in meiosis II until fertilization by the sperm. Fertilization triggers completion of meiosis II, resulting in a fertilized ovum (zygote) that is haploid. Does that help?

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  • Ae-Ri
    Ae-Ri Posts: 225

    Moderator

    🚨
    Answer ✓

    Hi Jacob

    At birth, the eggs are all halted in meiosis I, so they are all primary oocytes, which are diploid. Menses triggers the completion of meiosis I of the primary oocyte to result in the secondary oocyte, which is haploid. That secondary oocyte then holds in meiosis II until fertilization by the sperm. Fertilization triggers completion of meiosis II, resulting in a fertilized ovum (zygote) that is haploid. Does that help?

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