I usually hang out in the coding and maintenance forums but I feel the need to chime in here. Genetics is just an excuse people use to defeat themselves when trying to achieve their goals. I was genetically predisposed to be a 130lb 6' scrawny dude but I picked up lifting and I'm fast approaching 200lbs. I expect to pass that by December.
Besides an effective and evolving lifting routine, you must be truly dedicated to attaining your goals both inside and outside the gym. Lifting is important but it must be supported by a healthy and plentiful diet. The hardest part for me is fitting the required eating into my daily routine with work and all, so I make up for missed meals (I like to have 5 per day) with a weight gainer shake. Don't kill yourself, but try to come close to full whenever you eat. Also, watch what you eat. Cinnabons will help you gain weight but not the right kind. Eggs, milk, yogurt, and meats are all excellent sources of protein so eat these often and fat has nutritional value so don't eliminate fats entirely. In order to gain weight your caloric intake must exceed your caloric output and throwing complex carbs into the mix and help you with this. Also watch your alcohol intake, not only does alcohol contain a lot of empty calories, it also promotes estrogen production which you don't want.
No matter which muscle group you want to improve, it is always important to emphasize the compound lifts that hit multiple groups at the same time. For bigger biceps, pull ups (or pull downs) and bent over rows are a must. You can do many variations of these exercises so change it up periodically. After you have hit the large groups then focus on the smaller groups with your isolation exercises such as curls. I also can't stress enough the importance of hitting all of the major muscle groups. Skipping over legs because they don't penetrate your t-shirt is a big no-no. Squats and dead lifts are key to stimulating natural testosterone production because they work the largest muscles in your body. Higher testosterone will help you achieve gains in all areas.
Last, if you choose to incorporate supplements (which I recommend), do your homework and learn how and when to use them for maximum effectiveness. Protein is always good right after a workout because your muscles are looking for extra nutrients to help them recover. If you take a weight gainer formula, don't skip the gym because your body would love to turn those extra calories into fat. Creatine monohydrate can provide a helpful boost to get those few extra reps in and pre-workout energy formulas can be very effective. Just be sure to cycle on and off the pre-workouts because your body will develop a tolerance and their effectiveness will diminish if you don't. The recommended cycles can usually be found on the packaging.
I hope this helps, and don't let others' defeatist attitudes get you down!