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Sorry for the mistakes. Djokovic right now leads Federer by 2155 points, so it's entirely in Djokovic's racquet who will be number 1. Even if Djokovic doesn't play anything from now to the end of year, Federer still needs to earn 2155 points at least. That's not easy.
Actually I think the simplest way is to look at points earned from beginning of 2012 to now.
Djokovic had earned 11,410, Federer 9,255. So Djokovic is leading by more than 1000 points at this point. This means even if Federer wins everything from now to WTF, but if Djokovic can make finals, he'd still be number 1 by year end.
Djokovic is behind Federer less than 200 points right now, so Federer must win Basel and Paris just to keep his current points. But if Djokovic makes final in Paris, he will edge Federer just a bit even if Federer wins both Basel and Paris, and it will come down to the WTF to decide who's going to be number 1. I think that's a good scenario to have the final contest among the top 8 decides the world number 1.
"I want to know if federer will defend 1500 at london or these points are bonus and thanks."
This I don't have firsthand knowledge myself, but I've heard from several sources that these points are bonus. However, right now Djokovic trails Federer by less than 200 points, and Federer's points include the 1500 from last year. For this year, Djokovic has equal opportunity to earn those 1500 bonus points.
Thanks for your comment. I don't think Nole can break Federer's Slam record. If you notice, around Nole's age, Federer was winning three Slams a year for three years. After that he was still winning here and there, even now when he's 31. Federer was able to dominate like that for that long because he played at a higher level than the rest, a level that required some times for the rest to catch. Djokovic is very very tough right now, but he's not playing at a level a notch above his competitors, so I don't see how he could break Federer's Slam record.