The injuries and intrigue, passion for fashion, disdain for the tennis grind and insistence on go-for-broke strokes — all in the context of a friendly sibling rivalry — make even Mom reluctant to predict what the Williams sisters might do next.

They'd love to win Wimbledon, and Venus and Serena Williams will be among the favorites when the tournament begins Monday. But both have been erratic this year, raising anew questions about their devotion to a sport they once dominated.

"They have a lot of things going on with their life," said their mother and coach, Oracene Price. "Sometimes you never know what's going on in their head, especially girls."

The sisters are coming off a rare double defeat at the French Open, where they were eliminated in the third round. It was only the second time they lost on the same day at a Grand Slam event, which should stoke their desire for a strong showing at Wimbledon.

"We always learn and get more determined after a loss," Venus said.

Venus and Serena are in opposite halves of the draw, which means they could meet in the final, and grass often puts extra spring in their step. They've combined to win six of the past eight Wimbledon titles, and a return to the All England Club rejuvenated Venus' game last year, when she won the trophy for the fourth time and became the tournament's lowest-ranked women's champion at No. 31.

On the surface, it's easy to explain the sisters' success at Wimbledon: Lawn tennis suits their big serves, slam-bang groundstrokes and willingness to charge the net.

In addition, they find inspiration in the tradition that accompanies the tournament.

"Wimbledon, I think, has been around for hundreds of years," Serena said. "It doesn't get better than that."

It has actually been around since 1884, when another family dominated: Maud Watson beat sister Lilian in the final.

More than a century later, the world's oldest and most tradition-bound tennis tournament is in transition. A retractable roof over Centre Court is still a year from completion, but an overhead cover for fans is back after the ongoing project left them with no protection last year. Capacity has increased to 15,000 from 13,800.

A new Court 2 is nearly finished, and the old one will be used this year for the last time. That's good news for such players as the Williams sisters, because Court 2 has long been nicknamed the "Graveyard of Champions."

There are plenty of candidates to derail the sisters' title hopes this year, including French Open winner Ana Ivanovic, 2004 Wimbledon champion Maria Sharapova and even 1999 champion Lindsay Davenport, who is in the draw for the first time in three years.

On Tuesday, Ivanovic will play her first match as the world's top-ranked player.

"It's a great, great position and it's a dream coming true," she said Saturday. "But still I want to work hard and keep that position as long as I can."

On the men's side, Roger Federer remains No. 1 for the 229th week in a row, extending his record. He'll play the first Centre Court match to begin his bid for a sixth consecutive Wimbledon title. In the past 100 years, only Federer and Bjorn Borg (1976-80) have won five in a row.

But for the first time in several years, Federer appears vulnerable even on his favorite surface. A bout with mononucleosis slowed him early in the year, and against Rafael Nadal in the French Open final, Federer endured his most lopsided Grand Slam loss.

In addition, Federer faces the toughest draw of the top contenders. Possible opponents for him in the opening week include big-serving Robin Soderling and Fernando Gonzalez, 2007 quarterfinalist Tomas Berdych, 2002 champion Lleyton Hewitt and No. 5-seeded David Ferrer, who won his first grass-court title Saturday in the Netherlands.

Nadal is trying to become the first man since Borg in 1980 to win the French Open and Wimbledon in the same year. He was runner-up to Federer at Wimbledon each of the past two years, and last week Nadal became the first Spanish man in 36 years to win a grass-court title, defeating Novak Djokovic in the Queen's Club final.

An always-diplomatic Nadal said Federer remains the player to beat.

"Everybody says I'm one of the favorites," Nadal said. "The second Sunday of Wimbledon, we know who is going to be the favorite, no?"

The second Saturday of Wimbledon may well include a Williams.

Venus has reached the final in six of the past eight years, winning the title in 2000, '01, '05 and '07. She lost to her younger sister in the final in '02 and '03. Serena has eight major titles and Venus six, which makes them the leaders among active players on the women's tour.

But as always, there are questions about their focus and ability to stay healthy. Serena hasn't reached a Grand Slam final since winning the 2007 Australian Open; Venus hasn't reached a final of any kind since October.

They're usually less animated discussing tennis than talking about their latest design in tennis wear, or what they've been reading (Venus) or watching (Serena).

"Now I buy a lot of programs on iTunes," Serena reported during the French Open. "I just downloaded 'The Jeffersons' — you know, season five. I have a lot to watch."

Two days later, she shanked overheads, sprayed volleys and lost to Katarina Srebotnik. Mom conceded she was puzzled by the performance but expects Serena to "come out swinging" at Wimbledon after such a stinging defeat.

"Usually when she gets hurt like that, she's letting nothing stop her," Price said. "Maybe it's a good thing."

The same could be true for Venus, who looked listless in her Roland Garros loss to Flavia Pennetta but has a history of early round exits at Paris.

"Usually I'm extremely upset about the result, and then I work even harder," she said.

Recently retired Justine Henin is no longer a concern for the Williamses, but there are plenty of emerging youngsters to worry about. Last year the sisters were the oldest of the Wimbledon women's quarterfinalists, a group that included three teenagers.

Serena is 26, and Venus turned 28 on Tuesday. There's always speculation about how much longer they'll play, especially after performances like those at the French Open. Price said retirement's not on the horizon and predicted they won't quit at the same time.

"If I had to guess who would do it earlier: Serena," Price said. "She wants kids. She wants a family."

Another generation of Williamses? The family's domination at Wimbledon may be only beginning.

AP Tennis Writer Howard Fendrich contributed to this report.