Get Properties of baseclass and specific inherited class

I have a base class CrmObject and a few classes that inherit it (Aufgabe, Kontakt, ...). I only have a string-value for the child-class and I want to get both the Properties of CrmObject and the specific child-class in one Statement.

I'd get the properties of the child-class like this:

var propertyInfos = typeof(CrmObject).Assembly.GetType("Aufgabe").GetProperties().Where(p => Attribute.IsDefined(p, typeof(ImportParameter)));

But I'd like to get the Properties of CrmObject, too. Possibly within the same statement.