Three distinct classes of photoreceptors mediate the effects of UV-A/blue light (320–500 nm): the cryptochromes, phototropins and the ZEITLUPE (ZTL) family of proteins

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#Unit 5. Developmental Biology

Primitive Streak

The first morphological sign of gastrulation in amniotes

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#Id: 1584

#Unit 5. Developmental Biology

Primitive Streak; homologous to amphibian blastopore lip

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#Id: 1585

#Unit 5. Developmental Biology

Ability to initiate a primitive streak is found throughout the marginal zone.

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#Id: 1586

#Unit 5. Developmental Biology

Once the PMZ has formed, it prevent other regions of the margin from forming their own primitive streaks.

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#Id: 1587

#Unit 5. Developmental Biology

PMZ = Amphibian Nieuwkoop center

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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.