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Questions and Answers
What is the primary function of homologous recombination?
What is the primary function of homologous recombination?
- To prevent DNA replication by creating single-strand breaks.
- To facilitate the exchange of genetic material at specific DNA sequences.
- To introduce genetic diversity through random mutations.
- To maintain genomic integrity by repairing double-strand breaks. (correct)
Which of the following best describes a double-strand break (DSB)?
Which of the following best describes a double-strand break (DSB)?
- A break in the DNA backbone affecting a single strand, stalling DNA replication.
- A break in both strands of DNA that can halt replication and lead to cell death. (correct)
- A minor DNA lesion that does not significantly affect cellular processes.
- A repair mechanism that fixes single strand breaks and maintains the stability of DNA.
What triggers the occurrence of double-strand breaks during DNA replication?
What triggers the occurrence of double-strand breaks during DNA replication?
- The encounter of replication forks with a single-strand break in a template strand. (correct)
- The direct exposure of DNA to γ radiation.
- The presence of homologous sequences during DNA strand synthesis.
- The random insertion of new nucleotides during DNA replication.
How is homologous recombination related to recombinational DNA repair?
How is homologous recombination related to recombinational DNA repair?
Why are deficiencies in double-strand break repair systems linked to increased cancer risk?
Why are deficiencies in double-strand break repair systems linked to increased cancer risk?
Based on the content, what characteristic distinguishes homologous recombination from other forms of recombination, such as site-specific recombination?
Based on the content, what characteristic distinguishes homologous recombination from other forms of recombination, such as site-specific recombination?
What phenotype is commonly associated with genetic diseases caused by defects in homologous recombination and recombinational DNA repair?
What phenotype is commonly associated with genetic diseases caused by defects in homologous recombination and recombinational DNA repair?
What is the role of BRCA1 and BRCA2 proteins in relation to homologous recombination?
What is the role of BRCA1 and BRCA2 proteins in relation to homologous recombination?
What significant role does recombinational DNA repair play in diploid organisms?
What significant role does recombinational DNA repair play in diploid organisms?
Why is the capacity for enzymatic repair of DSBs considered essential for free-living organisms?
Why is the capacity for enzymatic repair of DSBs considered essential for free-living organisms?
What was the major cause of DNA damage that drove the evolution of DNA repair systems?
What was the major cause of DNA damage that drove the evolution of DNA repair systems?
Besides DNA repair, what other broad role has homologous recombination evolved to facilitate among populations of organisms?
Besides DNA repair, what other broad role has homologous recombination evolved to facilitate among populations of organisms?
What fundamental process is significantly linked to homologous recombination because it can also introduce double-strand breaks?
What fundamental process is significantly linked to homologous recombination because it can also introduce double-strand breaks?
What are the consequences for a mammalian embryo with a complete lack of capacity for repairing double-strand DNA breaks (DSBs)?
What are the consequences for a mammalian embryo with a complete lack of capacity for repairing double-strand DNA breaks (DSBs)?
What significant contribution did the study of homologous recombination provide to the field of genetics?
What significant contribution did the study of homologous recombination provide to the field of genetics?
In addition to DNA repair, which biological process do cellular recombinational systems sometimes participate in?
In addition to DNA repair, which biological process do cellular recombinational systems sometimes participate in?
How does recombinational DNA repair contribute to genetic diversity in eukaryotes?
How does recombinational DNA repair contribute to genetic diversity in eukaryotes?
What is a major consequence of DNA damage in aerobic organisms that was limited before the evolution of repair systems?
What is a major consequence of DNA damage in aerobic organisms that was limited before the evolution of repair systems?
Flashcards
Genetic Recombination
Genetic Recombination
The exchange of genetic information between chromosomes or segments.
Homologous Recombination
Homologous Recombination
Genetic exchanges at sequences that are nearly identical in DNA segments.
Double-Strand Break (DSB)
Double-Strand Break (DSB)
A severe DNA lesion that can lead to cell death if unrepaired.
DNA Repair Process
DNA Repair Process
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BRCA1 and BRCA2
BRCA1 and BRCA2
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Recombinational DNA Repair
Recombinational DNA Repair
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Genomic Instability
Genomic Instability
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Transposition
Transposition
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DSBs
DSBs
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Evolution of recombination systems
Evolution of recombination systems
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Oxidative DNA damage
Oxidative DNA damage
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Chromosomal crossovers
Chromosomal crossovers
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Genetic diversity
Genetic diversity
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Cell division accuracy
Cell division accuracy
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Fungal mating types
Fungal mating types
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Horizontal gene transfer
Horizontal gene transfer
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Study Notes
Genetic Recombination
- Genetic recombination is the exchange of genetic information between chromosomes or chromosomal segments. Several mechanisms are involved.
- Homologous recombination (HR) involves exchanges at sequences nearly identical in both DNA segments. Any shared sequence can suffice.
- Other forms of recombination exist, including those requiring specific sequences (site-specific recombination, some transposition) and those occurring almost randomly (some transposition).
Homologous Recombination as DNA Repair
- Homologous recombination is primarily a DNA repair process, focusing on double-strand breaks (DSBs).
- DSBs are the most dangerous DNA lesions, potentially lethal if unrepaired.
- DSBs often arise during DNA replication when replication forks encounter single-strand breaks in the template strand.
- HR and recombinational DNA repair are the same process carried out by the same enzymes.
Double-Strand Breaks (DSBs)
- DSBs are the most hazardous DNA lesions, stopping DNA replication.
- They can arise during DNA replication encountering a broken template strand, or exposure to UV light or gamma radiation.
- In mammals, inadequate DSB repair systems are linked to increased cancer risk. Examples include genes BRCA1 and BRCA2, associated with breast cancer.
- Defects in HR-related genes cause various human genetic diseases, exhibiting genomic instability, developmental abnormalities, light sensitivity, and cancer.
Evolutionary Significance of DNA Repair
- All free-living organisms possess the capacity for enzymatic DSB repair.
- This capacity likely evolved alongside the need to repair stalled replication forks.
- Spontaneous DNA damage is extremely common. Bacteria in oxidative environments experience thousands of lesions per cell per generation; mammalian cells suffer hundreds of thousands per 24 hours.
- Recombination systems evolved to deal with this extensive DNA damage, allowing organisms to successfully replicate large genomes in aerobic environments.
Recombination in Eukaryotes and Beyond
- In eukaryotes, recombinational DNA repair machinery ensures accurate chromosome transmission.
- Recombination during meiosis introduces DSBs in each chromosome and provides links between sister chromatids, ensuring their precise segregation.
- This process can generate chromosomal crossovers, exchanging large segments of genetic material between homologous chromosomes, increasing genetic diversity.
- Early genetics studies were inspired by the effect of recombination on inheritance.
- Recombination systems are essential tools in several cellular processes.
- HR is adapted for genetic adaptation by organisms in rapidly changing environments.
- Recombination is involved in processes like fungal mating type changes, bacterial immune evasion, and horizontal gene transfer.
- In short, homologous recombination is a vital mechanism for DNA repair, enabling accurate DNA replication, transmission of genetic information, and enabling adaptation in organisms.
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