第三基因突变精要.ppt

Generalized transduction allows the transfer of DNA from one bacterium to another at a low frequency. Specialized transduction can allow extremely efficient transfer while also allowing a small region of a bacterial chromosome to be replicated independently of the rest. Specialized Transduction Specialized Transduction Conjugation 接合 Bacterial Conjugation is genetic recombination in which there is a transfer of DNA from a living donor bacterium to a recipient bacterium. Often involves a sex pilus. Genetic map of the F plasmid and types in cells Hfr having an integrated F factor and characterized by a high frequency recombination strains. F- F- cells lack the F plasmid F+ Cells possessing an un integrated F plasmid are called F+. F’ If excision of F from the chromosome is not precise, a small section of host chromosome may be carried with the plasmid, creating an F’ (F-prime) plasmid. Types of F plasomid Donor bacterial that have the fertility gene (F gene) produce F pili. In F+ strains the F gene is on a plasmid. The F gene can be incorpo-rated into the bacterial chromosome to produce donor strains designated Hfr. Production of an F? factor The 3 conjugative processes I. F+ conjugation II. Hfr conjugation III. Resistance plasmid conjugation Mechanism of DNA Transfer I. F+ Conjugation Process F+ Conjugation- Genetic recombination in which there is a transfer of an F+ plasmid (coding only for a sex pilus) but not chromosomal DNA from a male donor bacterium to a female recipient bacterium. Involves a sex (conjugation) pilus. Other plasmids present in the cytoplasm of the bacterium, such as those coding for antibiotic resistance, may also be transferred during this process. II. Hfr Conjugation Genetic recombination in which fragments of chromosomal DNA from a male donor bacterium are transferred to a female recipient bacterium following insertion of an F+ plasmid into the nucleoid of the donor bacterium. Involves a sex (conjugation)pilus. III. Resistant