MEXICO CITY- A 20-year-old dancer from Japan was crowned Miss Universe 2007 on Monday night, marking only the second time her country has won the world beauty title.Dressed in a black, red and purple Japanese-style gown, Riyo Mori nervously grabbed the hands of first runner-up, Natalia Guimaraes of Brazil, just before the winner was announced. Then she threw her hands up and covered her mouth, overcome with emotion.But she gathered herself together enough to catch the diamond-and-pearl-studded headpiece valued at $250,000 as it slipped off her head when Miss Universe 2006 Zuleyka Rivera of Puerto Rico crowned her. Mori immediately placed it back on her head….