RB

Recording-2025-02-24T08_04_33.840Z

Developmental Biology

  • Definition: Study of how animals and plants grow and develop, focusing on animals in this context.

Key Question in Developmental Biology

  • How can a complete organism arise from a single, barely visible egg cell?

  • Transition from a single cell to an organism with millions of organized cells and complex mechanisms.

Historical Beliefs

  • Ancient belief: The organism was preformed in the egg (sperm contained a miniature version).

  • The developmental process was considered a mere increase in size.

Early Discoveries

  • Casper Friedrich Wolff: First to observe chicken embryos; observed no pre-formed chick but rather layers of cells.

Concept of Germ Layers

  • Proposed three germ layers in embryos: Ectoderm, Mesoderm, Endoderm.

  • Functionality is linked to each layer.

Ectoderm

  • External layer.

  • Forms:

    • Epidermis (skin covering).

    • Nervous system.

  • Connection between skin conditions and nervous issues due to shared embryonic origin.

Mesoderm

  • Intermediate layer.

  • Forms:

    • Muscles, soft internal organs, reproductive organs, bones.

    • Surrounds peritoneal cavity.

Endoderm

  • Most internal layer.

  • Forms:

    • Digestive tube, respiratory tube, urinary tube.

Embryonic Development Stages

  1. Fertilization: Fusion of male and female gametes.

  2. Cleavage: Zygote divides without increasing overall size.

  3. Gastrulation: Blastula forms, organizing into distinct layers.

  • Metamorphosis: A large developmental change (not present in all species).

Fertilization Process

  • Gametes are haploid; fusion creates a diploid zygote.

  • Fertilization initiates the differentiation process.

Parthenogenesis

  • Unfertilized eggs can develop into adults (e.g., in certain bees and amphibians).

Types of Hermaphrodites

  • Monoecious: Possessing male and female reproductive organs.

    • Cross-fertilization: Preferred for genetic diversity.

    • Self-fertilization: Last resort if partners are scarce (can lead to inbreeding problems).

  • Sequential Hermaphrodites: Change sex during their lifetime (e.g., clownfish).

Importance of Nutrients in Eggs

  • Egg cells provide nutritional substances (vitellus) necessary for embryo survival.

  • Size difference between species (e.g., chicken vs. human eggs).

Mechanisms in Fertilization

  • Specific Recognition: Ensures sperm from the same species fertilizes the egg via chemotaxis.

  • Avoiding Polyspermy: Prevents multiple sperm cells fertilizing one egg; involves changes in electric potential.

Summary of Early Stages

  • Cleavage: Zygote divides into smaller cells without increasing size (morula stage).

  • Blastula: Hollow ball of cells forms from morula.

  • Gastrulation: Ball of cells reorganizes into germ layers, paving the way for organogenesis.

Conclusion

  • Understanding these processes is crucial for studying developmental biology and recognizing potential issues in development.