Genetic analysis in bacteria and viruses are different than that in eukaryotes because bacteria and viruses have special genome organization, therefore different techniques and methods are used to analyze their genes and mutations. Because bacteria and viruses grow rapidly and make their DNA rapidly, they are often used as host cells or vectors in recombinant DNA technology. Study on bacterial and viral genetic system provides us insightful information about both of their pathology and their application in research and therapy.
Bacterial genetic material
Bacterial genetic material usually contains two parts: the bacterial chromosome and small circular double strand plasmid. The bacterial chromosome is one big loop attached to cell wall, also a circular molecule. It has one replication origin, and the replication follows semiconservative pattern. The plasmid has its own replication origin and the replication of plasmids is independent of the replication of chromosome.
Genetic analysis in bacteria
There are three ways of transfer genetic materials between bacteria: conjugation, transformation and transduction. Conjugation is the process of two bacteria close to each other and exchange genetic material; transformation is the process that bacteria pick up DNA from its surrounding environment. Transduction means the bacteria is infected by virus (phage) and gain genetic material there.
This can be done because of a plasmid in bacteria called F factor. F+ cells contain F factor and act as donors, while F- cells are recipients. During conjugation, F plasmid copies itself and gives a copy to the recipient, resulting in two F+ cells. When F plasmid is integrated into bacterial genome, they are called Hfr cells, which are also donors. Conjugation of an Hfr cell and an F- cell results in one original Hfr cell and one F- cell which may contain new DNA material from Hfr cell. This is the base of bacterial genetic analysis in early days.
Genetic analysis in bacteria
When Hfr cells are conjugated with F- cells, the genetic material are transferred in a specific orientation. This enables us to determine the gene order and recombination frequency in a group of genes, which is, indeed, the genetic mapping in bacteria. Genetic mapping can also be done via bacterial phage.
Bacterial Phage and viral genetics
Bacterial phage has two life cycles: lytic cycle and lysogeny cycle. During lytic cycle, the phage particles infect bacterial cells and lyse the cells, releasing more copies of infectious particles. During lysogeny cycle, the phage genome is integrated into bacterial chromosome and remains there, replicated and passed along with the bacterial genome. The lysogeny cycle can be induced into a lytic cycle. Mapping of phage genes is similar to the mapping of bacterial genes.
Animal viruses are similar to phages in almost all aspects, there are more versatile, having more complexed genome composition, and mutate very fast.