End-labelling of a gene probe at the 5′ end with alkaline phosphatase and polynucleotide kinase. 

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#Id: 1588

#Unit 5. Developmental Biology

Primitive Streak

First arises from a local thickening of the epiblast at the posterior edge of the area pellucida (Koller’s sickle)

By stage 2, the primitive streak cells form a third layer that lies between the hypoblast and epiblast cells.

 By stage 3, the primitive streak has become a definitive region of the epiblast, with cells migrating through it to become the mesoderm and endoderm.

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#Id: 1589

#Unit 5. Developmental Biology

Primitive Groove

A depression that forms within the primitive streak that serves as an opening through which migrating cells pass into the deep layers of the embryo.

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#Id: 1590

#Unit 5. Developmental Biology

Primitive groove is homologous to the amphibian blastopore

TLS Online TPP Program

#Id: 1591

#Unit 5. Developmental Biology

Hensen’s node (Primitive Knot)

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#Id: 1592

#Unit 5. Developmental Biology

A regional thickening of cells at the anterior end of the primitive streak

TLS Online TPP Program

#Id: 1593

#Unit 5. Developmental Biology

Hensen’s node is the functional equivalent of the organizer (dorsal lip of the amphibian blastopore)