London, Jul 25 (IANS): A record-equalling number of sibling pairings are to compete in the tennis competition of the London Olympics.

Four couples -- two sets of brothers and sisters each -- are to partake in the men's and women's doubles, respectively.

Two of the sibling sets are from the same country: Venus and Serena Williams, and Bob and Mike Bryan are from the US and both pairs are among the favourites to win gold at the Games.

The Bryan brothers, who are twins as well, are competing in their third Olympic Games. They won bronze at Beijing, but the 11-time Grand Slam champions would want to better their record.

The Williams sisters are the defending Olympic champions and both are also competing in the women's singles event at London 2012. Serena won her fifth Wimbledon singles title earlier in July, equalling her sister's record.

Along with their doubles gold in Beijing, the American sisters also picked up doubles gold 12 years ago in Sydney, while Venus tasted singles glory at the same Games.

The other brothers-in-arms are British duo Andy and Jamie Murray, who made their Olympic debut together in Beijing. Andy, the younger of the two, is also competing in the singles and will be hoping to perform better than at this year's Wimbledon championships when he lost to Roger Federer in the final.

Poland's Agnieszka Radwanska competed in Beijing and will play in the women's doubles in London with her younger sister Urszula, who is making her Olympic debut.

Agnieszka was runner-up at Wimbledon earlier this month, narrowly losing to Serena Williams in the final. Both the Radwanska sisters are also competing in the women's singles.

The sibling count should have been up to five, but Alona Bondarenko was forced to withdraw from the Olympics through injury. Still, her younger sister Kateryna will represent Ukraine in the women's singles.