If your primers are 25 bases in length and are located at position 520 and 1240 in your sequence, how big a PCR product do you expect? The location positions are for the 3' end of the primers.

To determine the size of the PCR product, we need to subtract the positions of the primers from each other and add the length of one primer to the result.

The first primer is located at position 520, and the second primer is located at position 1240. To get the size of the PCR product, we subtract the two positions:

1240 - 520 = 720

720 represents the distance between the two primers. However, this distance alone does not give us the size of the PCR product because we need to account for the length of one primer as well.

Since each primer is 25 bases in length, we need to add the length of one primer to the result:

720 + 25 = 745

Therefore, you would expect a PCR product size of approximately 745 bases.