Categories of Secondary Inductions
The secondary inductions are categorized into two types.
1) Instructive Interaction: In such type of an interaction the inducing tissue gives instructions to commit cells to a particular pathway of development.
2) Permissive interaction: Here, the responding cells are previously determined and are ready to commence differentiation in a specific direction but wait for a signal from the inducing tissue. In other words, they need induction from a different tissue so that their committed potential could be expressed.
Whether it is instructive interaction or permissive one the inducing tissue has a critical role to play in the developmental process. It should be kept in mind that in the inductive interactions two tissues are involved: one, which gives the inductive stimulus (the inducer) and the other which is induced to develop in a specific way (the responding tissue). Hence, the responding tissue must also be competent enough to receive the induction signals. In many examples the competence of responding tissue to the induction signals is limited to a specific time period during development.