Synthesis of Genes - There are two approaches available for the synthesis of genes:

(i) When the detailed structure of a gene is available, this gene can be synthesized by a purely chemical method as done by H.G. Khorana for the synthesis of gene for a tRNA (reported for the first time in 1970).

(ii) If the detailed nucleotide sequence of the gene is not available, one may utilize the RNA directed DNA polymerase enzyme for the synthesis of the gene in question in the form of complementary DNA (cDNA) from the mRNA of the gene isolated in its pure form. As discussed above, cDNA can also be used for isolation of a gene either 0) from DNA extracted from living cells utilizing the technique of Southern blot hybridization.

(iii) a genomic library.