Method for detecting variation in subject base sequence of nucleic acid, method for selectively inhibiting amplification of nucleic acid, and kit for implementing these

The purpose of the present invention is to provide: a simple method capable of detecting a variant gene at a lower variant gene content than the detection limit of the variant gene by a clip-PCR method; and a kit for implementing the same. Also provided are: a simple method whereby the amplification of a target base sequence can be selectively suppressed in a nucleic acid amplification reaction; and a kit for implementing the method. In a nucleic acid amplification reaction, a diallylamine-sulfur dioxide copolymer containing the following constituent unit is used as an enhancer for inhibition of nucleic acid amplification by a sandwich nucleic acid: a constituent unit (A) having a structure represented by general formula (I-a) or general formula (I-b) or a structure that is an acid addition salt thereof; r1 represents an alkyl group having 1-10 carbon atoms, a cycloalkyl group having 5-10 carbon atoms, or an aralkyl group having 7-10 carbon atoms, which may have a hydroxyl group, and constituent unit (B) havi