The present invention relates to methods of detecting the presence of a genetic polymorphism within two or more closely linked, homologous genes, for example α-thalassemia, in a sample using RT-PCR by subjecting the sample to separate amplification reactions using (a) a pair of forward and reverse primers specific for the head region of each of said two or more closely linked, homologous genes and (b) a pair of forward and reverse primers specific for the tail region of each of said two or more closely linked, homologous genes; and detecting and quantitating the amplification products relative to a control product.