5細(xì)菌的遺傳和變異e(完整版)
【正文】 ch code for two antigenically different flagellar antigens. The expression of these genes is regulated by an insertion sequences. In one orientation one of the genes is active while in the other orientation the other flagellar gene is active. Thus, Salmonella can change their flagella in response to the immune systems39。Bacterial Geics XiaoKui GUO PhD 第一頁，共四十二頁。 attack. Phase variation is not unique to Salmonella flagellar antigens. It is also seen with other bacterial surface antigens. Also the mechanism of phase variation may differ in different species of bacteria (. Neisseria。 Bacterial mutation ? Mutation rate ? Mutation and selectivity ? Backward mutation 第十四頁，共四十二頁。 Conjugation ? Transfer of DNA from a donor to a recipient by direct physical contact between the cells. In bacteria there are two mating types a donor (male) and a recipient (female) and the direction of transfer of geic material is one way。 R Plasmid 第二十八頁，共四十二頁。s genotype without affecting the rest of the chromosome. 4. The high frequency of transfer and the small region transferred allows finestructure mapping 第三十五頁，共四十二頁。 XiaoKui GUO PhD。 Origin of transfer。 The mechanism of specialized transduction 第三十七頁，共四十二頁。 Generalized Transduction ? Generalized transduction is transduction in which potentially any bacterial gene from the donor can be transferred to the recipient. 第三十頁，共四十二頁。 Physiological States of F Factor ? Autonomous (F+) – Characteristics of F+ x F crosses ?F bees F+ while F+ remains F+ ?Low transfer of donor chromosomal genes F+ 第二十二頁，共四十二頁。s chromosome. 第十五頁，共四十二頁。 Transposons (Tn) Transposons are transposable geic elements that carry o
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