Biology · MU Sofia

34. Fertilization. Interaction of maternal and paternal genomes.

Explains fertilization from sperm capacitation and egg-binding through the acrosomal and cortical reactions, pronuclear formation and the first mitotic division. It then covers why both parental genomes are needed, describing genomic imprinting, its DNA methylation mechanism, Prader-Willi and Angelman syndromes, epigenetic reprogramming and the maternal-to-zygotic transition. Gynogenetic and androgenetic embryos are compared, and four mnemonics summarise the steps and imprinting concepts.

Inside: 17 sections · 4 labelled pictures · 8 flashcards · 9 min

Topic 35 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 17 sections, about 1,282 words (9 min of reading), with 8 flashcards.

In this note

  1. Fertilization. Interaction of maternal and paternal genomes.
  2. The Journey and Activation of Sperm
  3. Structure of the Egg and Initial Contact
  4. Acrosomal Reaction and Sperm-Egg Fusion
  5. Blocking Polyspermy
  6. Changes in the Oocyte Post-Sperm Entry
  7. Changes in the Sperm After Entry
  8. Formation of the Zygote and First Cell Division
  9. INTERACTION OF MATERNAL AND PATERNAL GENOMES
  10. Requirement of Both Parental Genomes
  11. What Is Genomic Imprinting?
  12. Mechanism of Genomic Imprinting
  13. Imprinting Disorders
  14. Epigenetic Reprogramming After Fertilization
  15. Maternal-to-Zygotic Transition
  16. Experimental Evidence: Gynogenesis and Androgenesis
  17. MNEMONIC

Fertilization. Interaction of maternal and paternal genomes.

  • Fertilization is the biological process by which a sperm cell from a male and an egg cell from a female unite to form a single-cell zygote, the earliest form of a new individual.
  • It starts with the initial contact between sperm and egg and ends when the zygote undergoes its first mitotic division, forming two blastomeres.
  • In humans, this process occurs over a period of about 24 hours and takes place in the ampulla region of the fallopian tube.

The Journey and Activation of Sperm

  • After ejaculation, millions of sperm are deposited into the female reproductive tract, but only a few hundred reach the egg.
  • As sperm approach the egg in the fallopian tube, they undergo capacitation—a biochemical process that alters the sperm membrane and makes them capable of fertilizing the egg.
  • During this phase, sperm become hyperactivated, meaning their tail movements become stronger and more whip-like, enhancing their swimming force.
  • This hyperactivation is triggered by increased calcium ion influx into the sperm tail, a crucial event for penetrating the outer egg layers.
  • Sperm are guided towards the egg by chemotaxis, a process in which chemoattractants released by the cumulus cells surrounding the egg guide the sperm in the right direction.
  • The oviduct (fallopian tube) also acts as a filter and selector, allowing only the most competent sperm to reach the egg, and also begins influencing epigenetic modifications in the embryo, even before fertilization is complete.

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