How, you ask, could I possibly know that words I haven't created yet will have such things? It has to do with pronunciation. The gender of suffixes will have to match the gender of post-infixes; some of them will be attributed to voiced consonants such as VDGB, and therefore need to be followed by a Z or other voiced fricative, and some to silent consonants FTKP, and need to be suffixed by an S or other silent fricative. This all equates to 'Gender', especially if you're "conlanging" (is that a verb?) a SpeedTalk-class (Phonaesthemic) language.
This all should have occured to me earlier.