Why when disigning primers for RTPCR, you need to chose a region where introns a - (Feb/21/2014 )

Why when disigning primers for RTPCR, you need to chose a region where introns are in the middle?

Consider what your RT-PCR primers are recognizing. When you make cDNA, you are generating the transcript from RNA. By having the primers extend across the intron, you are guaranteeing that you are only reading the RNA expression levels and not any DNA that made it through your purification steps. Does this make sense?