Most efficient way to store a big DNA sequence?

Question

I want to pack a giant DNA sequence with an iOS app (about 3,000,000,000 base pairs). Each base pair can have a value A, C, T or G

Answer 1

Base pairs always pair up, so you should only have to store one side of the strand. Now, I doubt that this works if there are certain mutations in the DNA (like a di-Thiamine bond) that cause the opposite strand to not be the exact opposite of the stored strand. Beyond that, I don't think you have many options other than to compress it somehow. But, then again, I'm not a bioinformatics guy, so there might be some pretty sophisticated ways to store a bunch of DNA in a small space. Another idea if it's an iOS app is just putting a reader on the device and reading the sequence from a web service.