In allele specific PCR amplification..the objective is to acheive amplification of a specific allele from a set of alleles.. for different objectives.....for example
1) studying the presence of a specific allele in individuals of a population which might be linked to a particular condition...
2) to study expression of a specific allele or even a specific memeber of a multi-memebr gene family...
in these cases contribution and importance of a specific allele is possible to evaluate
regarding the Primer designing considerations....one should follow general guidelines for designing primers but special emphasis should be on the regions of differences between different alleles or members of a gene family.....once they are designed the specific primers should be evaluated for specificity first before actaully using for different applications