Transposons are portable genetic elements which can insert themselves at random into a plasmid or any chromosome independently of the host cell recombination system. It was discovered by Barbara Mc Clintock (1940) in maize and termed as jumping genes. Later Headges and Jacob termed them as transposons. Introns are nontranslated sequences within the coding sequence of a gene. Such sequences are transcribed into hnRNA but are then spliced out and are not represented in the message. The non-intron sequences of the gene are referred to as exons. Cistron sequence of nucleotides in a DNA molecule code for one particular polypeptide chain.