Starting with one double strand, how many double strands of DNA would you have

[Whenloveandhatecollide]

after 2 cycles of PCR? How do you get this answer?
and then can you use that to get the answer to these?
How many after 3 cycles?
How many after 4 cycles?
How many after 10 cycles?
How many after 20 cycles?
How many after 30 cycles?

[bradlepe]

The formula is:

x*(2^n), where n equals the number of cycles and x equals the starting number of double-stranded DNA molecules.

At the beginning (0 cycles), there's 1 molecule of DNA. 1*(2^0) = 1
After the first cycle, it's 1*(2^1) = 2 dsDNA molecules
...
After 30 cycles, it's 1*(2^30) = 1073741824 dsDNA molecules.

This assumes that each cycle is 100% efficient and none of the raw materials needed ever run out (i.e. primers and dNTPs).

[Adam]

Each cycle of PCR doubles that amount of double strands you have.

So if you started with 1 double strand of DNA.

Then after 1 cycle you would have: 1 * 2 = 2 double strands
after 2 cycles you would have 2 * 2 = 4 double strands
after 3 cycles you would have 4 * 2 = 8 double strands
after 4 cycles you would have 8 * 2 = 16 double strands

I hope by now you see the pattern. You can use simple algebra to express the above:

T = N * 2^C

Where T is your total number of double strands, N is your starting number of double strands and C is the number of cycles.

Hope this helps,

Adam