A labeled primer that is known to hybridize to human DNA at 60 different sites in the genome is used to prime human DNA for the PCR reaction. A six base pair sequence (GACATT) is used as an unlabelled return primer for this PCR reaction. The resulting solution (after 20 thermal cycles) is run on an electrophoresis gel. On the average, how long (in base pairs) will the DNA produced in the above PCR experiment be?

The information is not complete in the question to say clearly that how long will be the PCR amplified product. Firstly, it is mentioned that the primer sequence would bind to 60 different sites in the genome. So, there will be 60 different PCR products. Each PCR product could be of different length. This is because we don't know that what is the length of each gene which is going to be amplified in all those 60 cases. Therefore, it is not possible to say what would be the length (in base pairs) of each PCR product as well as the average length. More information is needed to conclude.