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Polarity in embryogenesis

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Title: Polarity in embryogenesis  
Author: World Heritage Encyclopedia
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Subject: Ectoderm, Developmental biology, NovoGen, Polarity, Polarization
Collection: Developmental Biology
Publisher: World Heritage Encyclopedia

Polarity in embryogenesis

An oocyte with poles depicted

In developmental biology, an embryo is divided into two hemispheres: the animal pole and the vegetal pole within a blastula.

The animal pole consists of small cells that divide rapidly, in contrast with the vegetal pole below it. In some cases, the animal pole is thought to differentiate into the later embryo itself, forming the three primary germ layers and participating in gastrulation.

The vegetal pole contains large yolky cells that divide very slowly, in contrast with the animal pole above it. In some cases, the vegetal pole is thought to differentiate into the extraembryonic membranes that protect and nourish the developing embryo, such as the placenta in mammals and the chorion in birds.

The development of the animal-vegetal axis occurs prior to fertilisation.[1] Sperm entry can occur anywhere in the animal hemisphere.[2] The point of sperm entry defines the dorso-ventral axis - cells opposite the region of sperm entry will eventually form the dorsal portion of the body.[1][3]

In the frog

See also

  1. ^ a b Gilbert SF. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000. Early Amphibian Development. Available from:
  2. ^ Wolpert, Lewis; Tickle, Cheryll; Martinez Arias, Alfonso (2015). Principles of Development (5th ed.). Oxford University Press. p. 149. Retrieved 12 October 2015. 
  3. ^ Angerer, Lynne M.; Angerer, Robert C. (February 2000). "Animal–Vegetal Axis Patterning Mechanisms in the Early Sea Urchin Embryo". Developmental Biology 218 (1): 1–12.  
  4. ^ P. Hausen, M. Riebesell: The Early Embryonic Development of Xenopus Laevis - An Atlas of the Histology ISBN 3-921ö15-ö4-9


The animal pole draws its name from its liveliness relative to the slowly developing vegetal pole. Hence the vegetal pole is named for its relative inactivity relative to the animal pole.



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