基因诊断技术 separate DNA DNA synthesis separate DNA DNA strands and anneal nynthesis primer separate DNA DNA strands and annea synthesis 聚合酶链反应 fragment of FIRST CYCLE SECOND CYCLE THIRD CYCLE (2double-stranded DNA molecles 4doubld DNAmo 18 double-stranded DNA molecules 13 基 因 诊 断 技 术 聚 合 酶 链 反 应