Step Five: Making Libraries of Genes

The mechanics of combining new DNA with plasmid vectors and placing these into bacteria makes it possible to clone any gene. But stop and think about where genes occur in nature. Genes will be found in all cells along with thousands of other genes that an organism has. When the DNA from an organism’s cells is extracted, all of the genes will be extracted together. A gene cloner will somehow need to sort through the 60,000 to 100,000 genes in a plant or animal in order to find the one gene they are interested in. This is done by making a large collection of bacteria colonies with cloned genes from the organism’s DNA and then sorting through the collection. This collection, called a library should be large enough to potentially contain a clone of every gene the organism has. There are two kinds of gene libraries, genomic and cDNA.