Download document

PowerPoint® Lecture Presentation for
Concepts of Genetics
Ninth Edition
Klug, Cummings, Spencer, Palladino
Chapter 6
Genetic Analysis and Mapping in
Bacteria and Bacteriophages
Lectures by David Kass with contributions from
John C. Osterman.
Copyright
© 2009©Pearson
Education,
Inc.
Copyright
2009 Pearson
Education,
Inc.
Section 6.1
• 6.1Bacteria 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
• 6.2Conjugation 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.5
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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.6
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.
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
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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.11
Section 6.4
• 6.4The 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.12
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
• 6.5Transformation 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.13
Section 6.6
• 6.6Bacteriophages 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.14
Copyright © 2009 Pearson Education, Inc.
Figure 6.15
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
• 6.7Transduction 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.17
Copyright © 2009 Pearson Education, Inc.
Figure 6.18
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
• 6.8Bacteriophages 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.
Copyright © 2009 Pearson Education, Inc.
Figure 6.19
Section 6.8
• Mapping in
Bacteriophages
• Mixed infection
experiments
demonstrated that
intergenic
recombination
occurs in
bacteriophages.
Copyright © 2009 Pearson Education, Inc.
Section 6.9
• 6.9Intragenic 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.
Copyright © 2009 Pearson Education, Inc.
The End
Copyright © 2009 Pearson Education, Inc.