c# assembly.GetExportedTypes

I am trying to get the type for the lowest class(G) in the chain of classes one inheriting from the other as shown below.

1.public class G: F

2.public class F: E

3.public abstract class E : D where TState : E, new()

4.public abstract class D :C

5.public abstract class C : IA, IB

6.public interface IA: IB

Additionally, I know only the type of IA all the rest is customer code which keep change.so knowing the type of IA I should get type of G

Currently I am using , var CLasstype= assembly.GetExportedTypes().Where(t => typeof(IA).IsAssignableFrom(t) && t.IsClass && !t.IsAbstract); This doesnt work for me for some reason.

Kindly help me out here Thanks