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#germ layers

4 public questions tagged with this topic.

amphibian Development-l

Gastrulation results in formation of:

Gastrulation converts radially symmetrical blastula into triploblastic gastrula through morphogenetic movements epiboly, emboly, involution, invagination, and convergent extension that reorganize cells without net growth. Animal cap ectoderm spreads over embryo, marginal zone mesoderm rolls inside over blastopore lip, and vegetal endoderm internalizes to line archenteron cavity. Molecularly BMP, Nodal, Wnt, and FGF pathways pattern germ layer identities before movements, with Nodal highest vegetally. End result is establishment of three definitive germ layers ectoderm, mesoderm, endoderm posit

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 21: Gastrulation forms three germ layers.

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Fertilization in mammals-ll

Epiblast cells eventually form:

After segregation of hypoblast, remaining inner cell mass cells constitute epiblast, a columnar pluripotent epithelium expressing Oct4 Nanog and Fgf4, forming embryonic disc. Epiblast gives rise to entire embryo proper through gastrulation generating definitive ectoderm, mesoderm and endoderm, while also producing amniotic ectoderm and extraembryonic mesoderm contributing to chorion and amnion. Hypoblast and trophoblast remain extraembryonic. Therefore epiblast represents founder population of fetal body, preserving developmental potency until gastrulation signals direct trilaminar differentia

Ref: Marikawa & Alarcon, Cold Spring Harb Perspect Biol: Epiblast origin of embryo proper and germ layer formation.

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Animal Classification

Diploblastic animals possess

Diploblastic animals possess only two primary germ layers formed during gastrulation: outer ectoderm giving rise to epidermis and nervous elements, and inner endoderm lining gastrodermis or gastrovascular cavity, with intervening acellular or sparsely cellular mesoglea not true mesoderm producing muscle. Cnidaria and Ctenophora exemplify this architecture, where epitheliomuscular cells derived from ectoderm and endoderm perform contraction, lacking coelom and mesodermally derived organs. Triploblasts add third layer mesoderm generating musculature, circulatory and skeletal tissues enabling com

Ref: NCERT Class 11 Chapter 4 Diploblastic Condition; Campbell Biology 12th ed. Chapter 32 Germ Layers

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