FIGURE 20.2 The Holliday model for homologous recombination. The Holliday model is adapted from R. Holliday (1964), A mechanism for gene conversion in fungi. Genet Res 5, 282–304. (b): From: H. Potter and D. Dressler, "DNA Recombination: In Vivo and In Vitro Studies," Sister chromatids ONLINE ANIMATION Homologous chromatids Cold Spring Harb Symp Quant Biol 1979. 43: 969-985, ©Cold Spring Harbor Laboratory Press. Image provided by Huntington Potter, Ph.D. a b CONCEPT CHECK: Explain why a heteroduplex region may be produced after branch migration occurs. 3' Both chromatids are nicked at 'identical locations. Nicks The DNA strands to the left of the nicks invade the homologous chromatids and covalently link to the strands to the right of the nicks. -Holliday junction The Holliday junction migrates from left to right. This is called branch migration. It creates 2 heteroduplex regions. (b) Micrograph of a Holliday junction Two heteroduplex regions that have a few base mismatches In this next step, the figure is simply redrawn by bending | the ends labeled A and B upward, and bending the ends labeled a and b downward. This makes it look more like a true Holliday junction. The Holliday junction is viewed in two different planes. End result A B в в The strands are Short connected to create nonrecombinant The strands that were originally nicked are broken. chromosomes with a short heteroduplex region. heteroduplex region a b Nonrecombinant chromosomes with a heteroduplex region Viewed in a different plane |(when rotated 180°) AB в, The strands that were not originally nicked are broken. в, The strands are connected Short heteroduplex region to create recombinant chromosomes with a short heteroduplex region. аь Recombinant chromosomes with a heteroduplex region (a) The Holliday model for homologous recombination
FIGURE 20.2 The Holliday model for homologous recombination. The Holliday model is adapted from R. Holliday (1964), A mechanism for gene conversion in fungi. Genet Res 5, 282–304. (b): From: H. Potter and D. Dressler, "DNA Recombination: In Vivo and In Vitro Studies," Sister chromatids ONLINE ANIMATION Homologous chromatids Cold Spring Harb Symp Quant Biol 1979. 43: 969-985, ©Cold Spring Harbor Laboratory Press. Image provided by Huntington Potter, Ph.D. a b CONCEPT CHECK: Explain why a heteroduplex region may be produced after branch migration occurs. 3' Both chromatids are nicked at 'identical locations. Nicks The DNA strands to the left of the nicks invade the homologous chromatids and covalently link to the strands to the right of the nicks. -Holliday junction The Holliday junction migrates from left to right. This is called branch migration. It creates 2 heteroduplex regions. (b) Micrograph of a Holliday junction Two heteroduplex regions that have a few base mismatches In this next step, the figure is simply redrawn by bending | the ends labeled A and B upward, and bending the ends labeled a and b downward. This makes it look more like a true Holliday junction. The Holliday junction is viewed in two different planes. End result A B в в The strands are Short connected to create nonrecombinant The strands that were originally nicked are broken. chromosomes with a short heteroduplex region. heteroduplex region a b Nonrecombinant chromosomes with a heteroduplex region Viewed in a different plane |(when rotated 180°) AB в, The strands that were not originally nicked are broken. в, The strands are connected Short heteroduplex region to create recombinant chromosomes with a short heteroduplex region. аь Recombinant chromosomes with a heteroduplex region (a) The Holliday model for homologous recombination
Human Anatomy & Physiology (11th Edition)
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Chapter1: The Human Body: An Orientation
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Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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Concept explainers
Genetic Recombination
Recombination is crucial to this process because it allows genes to be reassorted into diverse combinations. Genetic recombination is the process of combining genetic components from two different origins into a single unit. In prokaryotes, genetic recombination takes place by the unilateral transfer of deoxyribonucleic acid. It includes transduction, transformation, and conjugation. The genetic exchange occurring between homologous deoxyribonucleic acid sequences (DNA) from two different sources is termed general recombination. For this to happen, an identical sequence of the two recombining molecules is required. The process of genetic exchange which occurs in eukaryotes during sexual reproduction such as meiosis is an example of this type of genetic recombination.
Microbial Genetics
Genes are the functional units of heredity. They transfer characteristic information from parents to the offspring.
Question
In the Holliday model for homologous recombination shown, the resolution steps can produce recombinant or nonrecombinant
chromosomes. Explain how this can occur.
Transcribed Image Text:FIGURE 20.2 The Holliday model for
homologous recombination. The Holliday model is
adapted from R. Holliday (1964), A mechanism for gene
conversion in fungi. Genet Res 5, 282–304.
(b): From: H. Potter and D. Dressler, "DNA Recombination: In Vivo and In Vitro Studies,"
Sister chromatids
ONLINE
ANIMATION
Homologous chromatids
Cold Spring Harb Symp Quant Biol 1979. 43: 969-985, ©Cold Spring Harbor Laboratory
Press. Image provided by Huntington Potter, Ph.D.
a b
CONCEPT CHECK: Explain why a heteroduplex region may be produced
after branch migration occurs.
3'
Both chromatids are nicked at
'identical locations.
Nicks
The DNA strands to the left of the nicks invade
the homologous chromatids and covalently link
to the strands to the right of the nicks.
-Holliday junction
The Holliday junction migrates from left to
right. This is called branch migration. It
creates 2 heteroduplex regions.
(b) Micrograph of a Holliday junction
Transcribed Image Text:Two heteroduplex regions that
have a few base mismatches
In this next step, the figure is simply redrawn by bending
| the ends labeled A and B upward, and bending the ends labeled
a and b downward. This makes it look more like a true Holliday
junction. The Holliday junction is viewed in two different planes.
End result
A B
в
в
The strands are
Short
connected to create
nonrecombinant
The strands that
were originally
nicked are broken.
chromosomes with a
short heteroduplex region.
heteroduplex
region
a b
Nonrecombinant chromosomes
with a heteroduplex region
Viewed in a different plane
|(when rotated 180°)
AB
в,
The strands that
were not originally
nicked are broken.
в,
The strands are connected
Short
heteroduplex
region
to create recombinant
chromosomes with a short
heteroduplex region.
аь
Recombinant chromosomes
with a heteroduplex region
(a) The Holliday model for homologous recombination
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