How do the colonies in the library differ?
The bacteria colonies in our gene library will have nearly identical genetic makeups. Prior to transformation, they all originated from the same strain of bacteria, perhaps even from the same bacteria cell. Therefore they will all have the same genes in their bacterial chromosome (barring mutations). The bacteria all have a recombinant plasmid so they will have the gene sequences of the plasmid cloning vector in common. So what is different about them? The potential difference among bacteria in a gene library will be in the sequence of foreign DNA inserted into the recombinant plasmid. The screening methods used to identify the colony that has the gene of interest must be able to somehow detect that the bacteria cells possess the unique and desired sequence. The methods described will involve both the finesse of 'in situ' detection and the brute force of gene sequence databasing.