Copyright © 2009 Pearson Education, Inc. PowerPoint ® Lecture Presentation for Concepts of...

Copyright © 2009 Pearson Education, Inc.

PowerPoint® Lecture Presentation for

Concepts of GeneticsNinth EditionKlug, Cummings, Spencer, Palladino

Chapter 6Genetic Analysis and Mapping in

Bacteria and BacteriophagesLectures by David Kass with contributions from

John C. Osterman.Copyright © 2009 Pearson Education, Inc.


Section 6.1

• 6.1 Bacteria Mutate Spontaneously and Grow at an Exponential Rate

• Spontaneous mutation that occurs in the presence or absence of phage is considered the primary source of genetic variation in bacteria.


Section 6.1

• Selection is the growth of the organism under conditions in which only the mutant of interest grows well, whereas the wild type does not.


Section 6.1

• Prototroph • can synthesize all essential organic

compounds, and therefore can be grown on minimal medium.

• Auxotroph • through mutation, has lost the ability to

synthesize one or more essential compounds, and must be provided with them in the medium if it is to grow.


Section 6.1

• Bacteria have 4 phases when grown in culture: • lag phase• log phase (exponential growth)• stationary phase• death phase


microvet.arizona.edu


Section 6.2

• 6.2 Conjugation Is One Means of Genetic Recombination in Bacteria

• Bacteria undergo conjugation, in which• genetic information from one bacterium is

transferred to another • it recombines with the second bacterium’s

DNA


Section 6.2

• In bacterial conjugation in E. coli, F+ cells serve as DNA donors and F– cells are the recipients (Figure 6.6).

• F+ cells contain a fertility factor (F factor) that confers the ability to donate DNA during conjugation.

• Recipient cells are converted to F+.


Section 6.2

• An Hfr (high-frequency recombination) strain has the F factor integrated.

• An Hfr strain can donate genetic information to an F– cell, but the recipient does not become F+.


Section 6.2

• Interrupted matings demonstrated that specific genes in an Hfr strain are transferred and recombined sooner than others (Figure 6.7).


Section 6.2

• In some cases, an F factor is excised from the chromosome of an Hfr strain.

• In the process, the F factor (referred to as F’) often brings several adjoining genes with it (Figure 6.11).

• Transfer of an F’ to an F– cell results in a partially diploid cell called a merozygote.


Section 6.4

• 6.4 The F Factor Is an Example of a Plasmid

• Plasmids contain one or more genes and replicate independently of the bacterial chromosome (Figure 6.12).


Section 6.4

• F factors confer fertility.• R plasmids confer antibiotic resistance.• Col plasmids encode colicins that can kill

neighboring bacteria.


Section 6.5

• 6.5 Transformation Is Another Process Leading to Genetic Recombination in Bacteria

• In transformation, small pieces of extracellular DNA are taken up by a living bacterial cell and integrated stably into the chromosome (Figure 6.13).


Section 6.6

• 6.6 Bacteriophages Are Bacterial Viruses

• Bacteriophages can infect a host bacterium by injecting their DNA.

• Transduction • Type of bacterial genetic recombination

caused by the infection of a bacteriophage


Section 6.6

• Lysogeny occurs when: • the phage DNA integrates into the bacterial

chromosome• it is replicated along with the chromosome• it is passed to daughter cells

• Bacteria containing a prophage are lysogenic and can grow and divide stably until viral reproduction is induced.


Section 6.7

• 6.7 Transduction Is Virus-Mediated Bacterial DNA Transfer

• Bacteriophages, which can themselves undergo genetic recombination, can be involved in a mode of bacterial genetic recombination called transduction.


Section 6.7

• The Lederberg-Zinder experiment led to the discovery of phage transduction in bacteria (Figure 6.17).


Section 6.7

• In generalized transduction, bacterial DNA instead of phage DNA is packaged in a phage particle and transferred to a recipient host (Figure 6.18).

• In specialized transduction, a small piece of bacterial DNA is packaged along with the phage DNA.


Section 6.8

• 6.8 Bacteriophages Undergo Intergenic Recombination

• Phage mutations often affect plaque morphology (Figure 6.19 and Table 6.1).

• Such mutations have been important in understanding genetic phenomena in phages.


Section 6.8

• Mapping in Bacteriophages

• Mixed infection experiments demonstrated that intergenic recombination occurs in bacteriophages.


• 6.9 Intragenic Recombination Occurs in Phage T4

• Seymour Benzer’s (1950s) detailed examination of the rII locus of phage T4 allowed him to produce a genetic map of this locus.

Section 6.9


The End

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