Electron micrograph of the bacterium Escherichia coli which

Electron micrograph of the bacterium Escherichia coli, which has had its DNA released by osmotic shock.

Typical bacterial population growth curve showing the initial lag phase, the subsequent log phase where exponential growth occurs, and the stationary phase that occurs when nutrients are exhausted.

Genetic recombination of two auxotrophic strains producing prototrophs.

When strain A and B auxotrophs are grown in a common medium but separated by a filter, no genetic recombination occurs and no prototrophs are produced. The apparatus shown is a Davis U-tube.

Transmission electron micrograph of conjugating E. coli.

An electron micrograph of conjugation between an F+ E. coli cell and an F- cell. The sex pilus linking them is clearly visible.

1、 F因子（F-factor)的结构 配对区域(pairing region) 原点(origin) 致育基因 (fertility gene) F因子 原点(origin): (复制区) 配对区域(pairing region): (重组区) 致育基因(fertility gene): (接合转移区)

An F+×F- mating demonstrating how the recipient F- cell converts to F+.

The progressive transfer during conjugation of various genes from a specific Hfr strain of E. coli to an F- strain.

Conversion of F+ to an Hfr state occurs by integrating the F factor into the bacterial chromosome.

A time map of the genes studied in the experiment

4、 大肠杆菌染色体是环形的 Hfr H C J 4 P 72 o o thr azi lac tsx gal trp mal xyl met. B thi F tsx lac azi thr thi met. B xyl mal trp gal F thi met. B xyl mal trp gal tsx lac azi thr F met. B thi thr azi lac tsx gal trp mal xyl F Trp mal Gal xyl tsx C P 72 met. B H J 4 thi lac azi thr 不同Hfr菌株进行中断杂交实验， 基因转移的顺序、起点和转移方向 各不相同。 推断大肠杆菌的染色体为环形， 而F因子在细菌染色体上有许多插入 位点，且插入方向不同。

(a)The order of gene transfer in four Hfr strains, suggesting that the E. coli chromosome is circular. (b) The point where transfer originates (O) is identified in each strain.

1、 重组子的产生 lac+ ade+ strs lac+ ade+ strr lac- ade- strs lac+ ade+ strs lac- ade+ strr lac- ade- strr lac+ ade- strs

2、 重组频率的计算 RFlac-ade = = lac-ade+ lac+ade++lac-ade+ 220 1000 *100%=22%=22 c. M 1分钟相当于20%重组值，即： 1 min=20 c. M

The E. coli genome.

九、 F’因子和性导 Adel berg ，1959年 F’因子(F-primer factor) 性导(sex-duction or F’-duction)

Conversion of an Hfr bacterium to F’ and its subsequent mating with an F- cell.

The structure of bacteriophage T 4 including an icosahedral head filled with DNA, a tail consisting of a collar, tube sheath, base plate, and tail fibers.

Life cycle of bacteriophage T 4.

The plaque assay for bacteriophage analysis.

Electron micrographs of phage lambda (left) and the DNA isolated from it (right).

The Lederberg-Zinder experiment using Salmonella.

Generalized transduction.

Electron micrographs of phage lambda (left) and the DNA isolated from it (right).

• 附着位点（attachment site , att ） att B（又叫attλ）， att P • 正常的切离 • 非正常切离 • λdg(λd gal) • λdgal • λdbio • 低频转导(low-frequency transduction, LFT） • 高频转导(High-feequency transduction, HFT)

Proposed steps for transforming a bacterial cell by exogenous DNA.