Orthogenesis - “Straight-line evolution,” held that the variation that arises is directed toward fixed goals.

So that a species evolves in a predetermined direction by some kind of internal drive, without the aid of natural selection.

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#Unit 5. Developmental Biology

Oskar mRNA becomes complexed to kinesin I, a “plus-directed” motor protein that moves it toward the growing end of the microtubules at the posterior region, where Oskar protein can bind nanos mRNA

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#Unit 5. Developmental Biology

The inhibition of Oskar translation is mediated by two proteins- 

Bruno

Cup

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#Unit 5. Developmental Biology

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#Unit 5. Developmental Biology

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#Unit 5. Developmental Biology

An anterior-to-posterior gradient of Bicoid protein

An anterior-to-posterior gradient of Hunchback protein

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#Unit 5. Developmental Biology

A posterior-to-anterior gradient of Nanos protein A posterior-to-anterior gradient of Caudal protein