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.
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.
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc.
Section 6.1
• Bacteria have 4 phases when grown in culture: • lag phase• log phase (exponential growth)• stationary phase• death phase
Copyright © 2009 Pearson Education, Inc.
microvet.arizona.edu
Copyright © 2009 Pearson Education, Inc.
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
Copyright © 2009 Pearson Education, Inc. Figure 6.5
Copyright © 2009 Pearson Education, Inc.
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+.
Copyright © 2009 Pearson Education, Inc. Figure 6.6
Copyright © 2009 Pearson Education, Inc.
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+.
Copyright © 2009 Pearson Education, Inc.
Section 6.2
• Interrupted matings demonstrated that specific genes in an Hfr strain are transferred and recombined sooner than others (Figure 6.7).
Copyright © 2009 Pearson Education, Inc. Figure 6.7
Copyright © 2009 Pearson Education, Inc. Figure 6.8
Copyright © 2009 Pearson Education, Inc. Figure 6.9
Copyright © 2009 Pearson Education, Inc. Figure 6.10
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc. Figure 6.11
Copyright © 2009 Pearson Education, Inc.
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).
Copyright © 2009 Pearson Education, Inc. Figure 6.12
Copyright © 2009 Pearson Education, Inc.
Section 6.4
• F factors confer fertility.• R plasmids confer antibiotic resistance.• Col plasmids encode colicins that can kill
neighboring bacteria.
Copyright © 2009 Pearson Education, Inc.
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).
Copyright © 2009 Pearson Education, Inc. Figure 6.13
Copyright © 2009 Pearson Education, Inc.
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
Copyright © 2009 Pearson Education, Inc. Figure 6.14
Copyright © 2009 Pearson Education, Inc. Figure 6.15
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc.
Section 6.7
• The Lederberg-Zinder experiment led to the discovery of phage transduction in bacteria (Figure 6.17).
Copyright © 2009 Pearson Education, Inc. Figure 6.17
Copyright © 2009 Pearson Education, Inc. Figure 6.18
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc.
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.
Copyright © 2009 Pearson Education, Inc. Figure 6.19
Copyright © 2009 Pearson Education, Inc.
Section 6.8
• Mapping in Bacteriophages
• Mixed infection experiments demonstrated that intergenic recombination occurs in bacteriophages.
Copyright © 2009 Pearson Education, Inc.
• 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
Copyright © 2009 Pearson Education, Inc.
The End