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Unit 14: Embryonic Development and its Regulation

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    Embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal developmentdescribe later stages. Embryogenesis starts with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon).

    • 14.1: Embryonic Development
      This page outlines embryonic development in animals, which includes four stages: Cleavage (rapid cell division of the zygote), Patterning (cell organization and body axis establishment), Differentiation (activation of zygotic genes for specific cell types), and Growth. It emphasizes the transition from maternal mRNA to the embryo's genome. Research on frogs and snails illustrates the significance of mRNA distribution and protein gradients during early development.
    • 14.2: Frog Embryology
      This page describes the development of frog eggs into tadpoles. After fertilization, the zygote undergoes cleavage and forms a blastula with smaller cells. Gastrulation creates germ layers for body tissues. The Spemann organizer prompts ectoderm development into neural tissue, essential for the brain and spinal cord. The tadpole hatches as a complete structure and continues to grow by feeding, incorporating organic matter.
    • 14.3: Cleavage
      This page describes cleavage as a crucial early stage of cell division in embryo development post-fertilization, differentiating between holoblastic cleavage (complete division in low-yolk eggs like frogs) and meroblastic cleavage (incomplete division in high-yolk eggs like birds). It highlights how meroblastic cleavage occurs in a limited cytoplasmic region, resulting in multiple nuclei and a significant yolk mass, which aids in forming a normal-sized embryo from the fertilized egg.
    • 14.4: The Organizer
      This page explains the embryonic development of a zygote, highlighting the role of mRNA and protein gradients in determining cell fates, alongside intrinsic signals and cell interactions. It details the Spemann organizer's role in gastrulation and parallels with Drosophila development, emphasizing the formation of various organs such as wings, legs, and eyes. Overall, the development process encompasses axis establishment, body part formation, and detail refinement.
    • 14.5: Segmentation - Organizing the Embryo
      This page details the segmentation of Drosophila melanogaster, which features 14 body segments (3 head, 3 thoracic, 8 abdominal). The segmentation is controlled by maternal mRNA gradients, particularly bicoid and nanos, influencing genes like hunchback and even-skipped. These gradients function as transcription factors, facilitating gene activation patterns crucial for segment formation.
    • 14.6: Homeobox Genes
      This page examines the evolutionary conservation of eye development through the eyeless gene in Drosophila and the small eyes gene in mice, highlighting the role of selector genes in regulating embryonic development across species. Hox gene clusters, which include essential homeobox genes, are pivotal in forming complex structures. While these genes have maintained their functionality over millions of years, the resulting structures vary due to species-specific genes.
    • 14.7: Stem Cells
      This page covers stem cell classifications (totipotent, pluripotent, and multipotent) and their potential in treating cell damage, while addressing challenges like immunological rejection.
    • 14.8: Embryonic Stem Cells
      This page explores the properties and applications of human embryonic stem cells, including their role in cloning and regenerative medicine. It emphasizes their potential for understanding human development but notes ethical concerns regarding the destruction of blastocysts and challenges in ensuring compatibility for cell replacement therapies.
    • 14.9: Germline vs. Soma
      This page discusses the difference between mutations in somatic cells and germline cells. Somatic mutations, occurring in non-reproductive cells like liver cells, are not inherited and die with the individual. In contrast, germline mutations in sperm and eggs can be passed to future generations, making them significant in genetic inheritance. Understanding this distinction is crucial for comprehending how genetic information is transmitted across generations.
    • 14.10: Regeneration
      This page discusses the regenerative abilities of flatworms and salamanders, highlighting that flatworms use pluripotent stem cells (neoblasts) and Wnt/β-catenin signaling for regeneration, while salamanders rely on stem cell migration and dedifferentiation. In contrast, mammals have limited regeneration, mostly in skin and liver. The research on regeneration genes, particularly Wnt, indicates possibilities for enhancing regenerative processes in other species.

    Thumbnail: Human embryo, 8-9 weeks, 38 mm. (CC BY-SA 3.0; Anatomist90).

    This page titled Unit 14: Embryonic Development and its Regulation is shared under a CC BY 3.0 license and was authored, remixed, and/or curated by John W. Kimball via source content that was edited to the style and standards of the LibreTexts platform.