genetic disease polygenic vs. monogenic

[mellybelly]

We need some classification of inheritance patterns, this should relate existing classes. Not sure which ontology or where this goes, but something like this:

inheritance pattern --polygenic --monogenic ----dominant ----recessive etc. --no inheritance pattern (not sure what to call this but we need to be able to classify diseases where there is no known genetic inheritance pattern).

@nlwashington @pnrobinson @mbrush thoughts?