If, for example, Sarah Palin had many identified "high IQ genes" I doubt that the mainstreem media would have been able to characterize her as a dullard.
This assumes no correlation between whether she's a dullard and whether she sounds like one when she talks. I assume that this hypothetical non-dullard version of Sarah Palin would also not have been able to be characterized as a dullard because she wouldn't have said all the things that she said, thereby appearing to anyone who was paying attention to be a dullard.
You seem to be implicitly accepting the left's view of Palin. Many Republicans thought that the way she spoke indicated that she was smarter than Joe Biden.
I wrote an article for h+ predicting that the rapid fall in the cost of gene sequencing will allow U.S. voters to learn much about presidential candidates' DNA. The candidates won't be able to stop this because:
DNA analysis has a decent chance of reducing political bias by providing objective information about candidates. If, for example, 70% of the variation in human intelligence is determined by identified genes then DNA analysis would reduce disagreements among informed voters over a candidate's intelligence.