Microorganisms have the ability to acquire genes and thereby undergo the process of recombination. In recombination, a new chromosome with a genotype different from that of the parent results from the combination of genetic material from two organisms. This new arrangement of genes is usually accompanied by new chemical or physical properties.
In microorganisms, several kinds of recombination are known to occur. The most common form is general recombination, which usually involves a reciprocal exchange of DNA between a pair of DNA sequences. It occurs anywhere on the microbial chromosome and is typified by the exchanges occurring in bacterial transformation, bacterial recombination, and bacterial transduction.
A second type of recombination, called site-specific recombination, involves the integration of a viral genome into the bacterial chromosome. A third type is replicative recombination, which is due to the movement of genetic elements as they switch position from one place on the chromosome to another.
The principles of recombination apply to prokaryotic microorganisms but not to eukaryotic microorganisms. Eukaryotes exhibit a complete sexual life cycle, including meiosis. In this process, new combinations of a particular gene form during the process of crossing over. This process occurs between homologous chromosomes and is not seen in bacteria, where only a single chromosome exists. Much of the work in microbial genetics has been performed with bacteria, and the unique features of microbial genetics are usually those associated with prokaryotes such as bacteria.