Swiss investment bank UBS says a 31-year old trader lost $2 billion — all on his own with bad deals. Born in Ghana, and the son of a former UN official, Kweku Adoboli appeared in a London court today on fraud and false accounting charges. UBS claims he wrote an e-mail admitting he lost the money on bad trades. Allegedly, it took months, but nobody at the bank noticed anything wrong. UBS stocks are down more than 10 percent today and ratings agencies are warning about a possible downgrade. David Weidner is Wall Street columnist for MarketWatch.com and the Wall Street Journal.