Whenever a PCR is done, we have to use housekeeping genes like GAPDH, to self normalise the values to account for different starting cDNA/DNA. Now there are many different genes like GAPDH, ubiquitin, actin etc.
Now when dealing with cells, I can understand that due to their immortal nature and frankly shocking number of generations undergone by them, the expression of the housekeeping gene may change.
Assuming that I am not dealing with cells and instead with animal tissues, does it matter which house keeping gene I select? Or in other words is GAPDH going to give me the same consistency between samples as something like 18s Ribsomal RNA or am I missing something specific?