I have some bad genetics. I've been working hard to lose body-fat and gain muscle, and i've been pretty successful, but i'm still skinny. It's gonna take some time to get more mass through working out, so i want to know how i can gain more mass without gaining any fat. I blame my father for his terrible genetics. I lost about 5kilos of bodyfat, but i need to gain in back (and more) in muscle. any advice?

(btw - I was never obese or anything, i just had a bit of flab over my belly on my chest. I still do, but it's not as bad as it used to be)