Question

why does designing exon-spanning primers enables allows for the elimination of genomic DNA amplification during a real-time PCR reaction.

Answer 1

Exon spanning primers are specific for exon sequences. In can be one exon spanning primers or two exon spanning primers. The spanning region of exon is the region that will end near the intonic start region. Actually in spiced DNA it is a region of nearest exon (because in spiced DNA introns are spiced out from DNA sequences). Introns are actually the genomic DNA of non coding sequences. Exon spanning primers can only amplify the exon sequences not introns. Hence if there is any genomic DNA or contaminated genomic DNA is present in sample, it will not be amplified by RT-PCR exon spanning primer. So the genomic DNA or contaminated DNA will be eliminated.