I honestly don't believe it is only genetic, just from personal experience. I say that because my mom has them on her stomach, but I don't. She also gained about 50lbs during pregnancy, while I gained about 35lbs. If you want to know my honest thoughts on it, I think stretch marks are more so from gaining weight quickly rather than just because of the genetic factor. I say this because I had none until my body gained more rapidly during the last 4 weeks, and when I got them, I only a few on one of my thighs. None on my stomach. I am built differently than my mom and I also have a petite frame. I was about 130lbs and 5-4 and 1/2 pre pregnancy. Even though my mom is only about 1-1/2 inches taller than me, she carries her weight differently and looks too skinny at 130lbs.
I used bio oil for 2 weeks around the 20 week mark, but had to stop as I developed a rash. I also tried to use the Palmer's body butter toward the 7th month, developed a really bad rash, and had to stop that too. I just used Vitamin E serum as it didn't cause any issues.
During puberty, I got some small ones on my hips and thighs; again, from gaining a good 25 or so pounds in a year.
My suggestion is to eat well and stay hydrated. Don't use pregnancy as an excuse to eat poorly or binge, (some people do this--my mom included) and you will give yourself the best chance of gaining at a slower, more gradual rate. Please also don't not eat to keep from gaining. I would have a healthy snack whenever I felt a bit nauseous--banana, water; or crackers and a bit of cheese. Even at 3am.