To get this thread back on topic.
Do genetics play a roll in "talent/performance"? Yes.
Are genetics the deciding factor in how successful an athlete can be? No.
Sure there are people who are just "built" for certain sports. As a strength coach at various universities, there are always the freaks -
18 years old, 300lbs, 6'6", run a 4.8 40, clean and press 300+ without ever having trained in the weight room. Sure these people exist. There are, however, not that many of them.
Most are average "talent" and had good "training" early on, (read: played sports at a young age, were in martial arts/gymnastics at a young age, or were just significantly more active than other kids) and acquired a strong base to build off of.
Having seen some of these "gifted" people. Many do not really reach their full potential given that they never had to try that hard, up to a certain point.
On the flip side. There are many, MANY, less "talented" people who learn how to train, learn, work, and get the most out of what they have. These people often catch and surpass the "genetically gifted".
Every once in a while we will see a truly "gifted" athlete who has embraced their training and strives to be the best they can be. This is when we see something really special.
As many of you have seen in the past, I am not really big on the genetics thing. Mostly because, in real life, it does not matter. There is no way to know what we are genetically destined to be. Sure there is genetic testing, but that is never extensive enough to tell what lies ahead in an athletes career. Who says that we are even testing for the right things? Once we find out, does that mean that we press on, or give up? Most will not give up, so knowing has no bearing on what might happen anyhow.
Sure, there are some people who are in the shallow end of the gene pool and who, despite their efforts, are not likely to be impressive specimens. There are about as many of them as there are of the 300lb gorilla I described in the beginning of this post. There are also countless examples of how someone beat the odds.
The vast majority of us fall in between the shallow end and the deep end, since nobody knows exactly were we "should" be, most, given the right environment, can get much farther than the naysayers are willing to admit.
"Most" athletes are here to prove that more can be achieved if the mind is in the right place than if the genetics happen to be there. "Most" of the time, that is a true statement.