If we're talking about people and professions, yes. In general, you have to be more careful. It's still a good heuristics but you can't just look at the end of a word and deduce the gender. Especially chemical substances often are neuter and end in 'in'
- Das Aspirin
- Der Hermelin
So to distinguish the biological gender we use -in for people and professions. Is it the same case for animal kingdoms, e.g Der Hund - The dog, Die Hunde - The dogs, Die Hundin - The dog(female) Die Hund(e)innen - The dogs(female) or is there anything like male dog, female dog as in English?