Expressed sequence tag (EST): a cDNAplugin-autotooltip__default plugin-autotooltip_bigComplementary DNA (cDNA): DNA that has been reverse transcribed from spliced mRNA using reverse transcriptase. cDNA sequences are useful because they lack intron sequences and therefore contain information about the ORF of intron-containing eukaryotic genes. from a cDNA libraryplugin-autotooltip__default plugin-autotooltip_bigcDNA library: a library that is created from an mRNA sample, usually from a specific tissue source and/or cell type. The mRNAs, representing all the different genes that are expressed in that tissue, are reverse transcribed into cDNAs, which are then cloned and archived for research. that has been sequenced and catalogued.