Biology · MU Sofia

36. Embryonic development – early stages (zygote to neurula).

Walks through early embryonic development from zygote formation through cleavage, morula, blastula and gastrulation to neurulation and somite formation. It contrasts mosaic and regulative development, explains morphogens and ooplasmic segregation with the frog grey crescent, and describes amphibian organiser experiments. It also compares amniotes with anamniotes, lists the extraembryonic membranes of the amniotic egg, and gives four mnemonics for the stages, gastrulation movements, membranes and neural structures.

Inside: 20 sections · 2 labelled pictures · 10 flashcards · 6 min

Topic 37 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 20 sections, about 861 words (6 min of reading), with 10 flashcards.

In this note

  1. Embryonic development - early stages (zygote to neurula)
  2. General Framework of Embryogenesis
  3. Zygote
  4. Cleavage
  5. Morula
  6. Blastula
  7. Gastrulation
  8. Organogenesis
  9. Neurulation Process
  10. Neural Crest Cells
  11. Somite Formation
  12. Mosaic versus Regulative Development
  13. Morphogens and Ooplasmic Segregation
  14. Example of Ooplasmic Segregation in Frogs
  15. Experimental Manipulations in Amphibians
  16. Amniotes versus Anamniotes
  17. Structure of the Amniotic Egg
  18. MNEMONICS
  19. 🧫 3. Extraembryonic Membranes of the Amniotic Egg
  20. 🧠 4. Neural Development Structures

General Framework of Embryogenesis

  • Embryonic development occurs within protective structures like egg envelopes or the maternal placenta.
  • The development process culminates in either hatching (in egg-laying animals) or birth (in mammals).
  • Development can be of two types:
  • Indirect development involves a larval stage that later metamorphoses into the adult form. This is common in fish and amphibians.
  • Direct development skips the larval stage, where the embryo forms directly into a juvenile resembling the adult. This occurs in reptiles, birds, and mammals.

Stages of Early Embryogenesis

Zygote

  • The very first stage of development.
  • Formed by the fusion of a sperm and egg cell.
  • It is a single, diploid cell that marks the beginning of a new organism.

Cleavage

  • A rapid series of mitotic divisions that divides the zygote into smaller cells known as blastomeres.
  • These early divisions alternate between mitosis and DNA synthesis with no gap phases (G1 and G2).
  • Controlled by Mitosis Promoting Factor (MPF), a complex of cyclin B and the enzyme Cdc2.
  • MPF is essential and sufficient to push cells through the cell cycle in early development.
  • As cleavage progresses, cells eventually require gap phases to replenish cellular materials.

Continue reading free

The whole note, all 20 sections, is free with an AceMed account, with its 10 flashcards. Premium adds flashcard recall, highlights and Ask AI.

Start freeAlready a member? Open the note