Expressivity

Degree to which a trait is expressed.

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If Pax6 is lost (fruit flies, frogs, rats, humans) complete loss or reduction of the eyes

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#Unit 5. Developmental Biology

Two major modes of inductive interaction:

 Instructive interaction

 Permissive interaction

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#Unit 5. Developmental Biology

In instructive interaction, 

a signal from the inducing cell is necessary for initiating new gene expression in the responding cell.

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#Unit 5. Developmental Biology

Instructive interaction

It occur where the responding cell has a choice of fates and will follow one developmental pathway following induction and an alternative pathway in absence of the inductive signal. 

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#Unit 5. Developmental Biology

In Permissive interaction

The responding tissue has already been specified and needs only an environment that allows the expression of these traits. 

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#Unit 5. Developmental Biology

Epithelial-mesenchymal interactions

the interactions of sheets of epithelial cells with adjacent mesenchymal cells.