Yes, there definitely are genetic limits to a persons potential, be it physical or intellectual - it's just how we're wired.
Think bodybuilding, theres only a certain amount of muscle a person can develop in their lifetime. (Ignoring roids) or Runners for example, The types of muscle fibres we have in our bodies are either fast twitch or slow twitch fibres. Certain ethnicities may predominately have an abudance of one type of fibre which may lead them to excel at sprinting or Endurance respectively.
Of course, for the average athlete training would have the biggest impact but for individuals at their genetic limit, one with a better limit in the first place will succeed!
Of course that's science based, but you could argue that they're gifted