Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Substractive hybridization is a technology that allows for PCR-based amplification of only cDNA fragments that differ between a control and experimental transcriptome. Differences in relative abundance of transcripts are highlighted, as are genetic differences between species. The technique relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs or gDNAs of similar abundance, and retaining differentially expressed, or variable in sequence, transcripts or genomic sequences.