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Venus & Serena Williams

Tennis players Venus and Serena Williams are arguably the best-known sibling athletes in the world. Venus has won the Grand Slam title seven times and Serena has won it thirteen times, and on eight of these occasions they competed against one another. After all, they had knocked out everyone else. Each has been ranked number one in the world, so they make a formidable Doubles team, and they have taken top honors at the 2010 French Open.

The likelihood of one set of parents producing two such star athletes is slim --- so slim in fact that in 2002, The New York Times likened it to “one set of parents raising Picasso and Monet.” The sisters were trained by their father from an early age, and although they have an intense professional rivalry, it’s not so intense that one won’t show some sisterly support by watching the other one play.

Jewel Samad | AFP | Getty Images