Origins of Variation in Genomes Flashcards
Give an overall summary of mitosis:
- Somatic cells
- 2n –> 2n + 2n
- (1n –> 1n + 1n, in haploid organisms)
- Genetically identical daughter cells
Give an overall summary of meiosis:
- Haploid gamete production
- 2n –> n x 4
- Genetically different daughter cells
What happens to homologous chromosomes during mitosis?
Remain separate throughout
What happens to homologous chromosomes during meiosis?
Pair and recombine
At which stage of meiosis I does homologous recombination occur?
Prophase
Is the DNA replicated at the prophase of meiosis I?
Yes
What is another way to describe homologous recombination?
Crossing over
What is visible crossing overs known as?
Chiasmata
What is homologous recombination?
- Breakage and joining of DNA
- Reciprocal
- Genetic rearrangement
How does meiotic homologous recombination generate crossovers?
- Enzyme Spo 11 and Mre 11 nuclease complex cuts one of the double stranded chromosomes
- Repaired DNA double strand by either non homologous end joining or homologous recombination
How is DNA double strand breaks repair by non homologous end joining?
- Loss of nucleotides due to degradation from ends
- Blunt joining of ends
- Deletion of DNA sequence has occurred
How is DNA double strand breaks repair by homologous recombination?
- 2 different sisters chromatids
- Loss of nucleotides due to degradation from ends
- End processing and homologous recombination
- Damage repaired by using information from sister chromatids
Which out of non homologous and homologous recombination are a universal process?
Homologous recombination
Describe in detail DNA double strand breaks repair by homologous recombination:
- Double strand break
- Exonuclease degrades 5’ ends and creates 3’ overhang
- Strand invasion causes branch point known as heteroduplex structure (D-loop)
- DNA synthesis and migration of branch point where the 3’ overhang is being repaired on double strand
- Continued branch migration followed by pairing of newly synthesis DNA with top strand and top strand of DNA synthesis
- DNA ligation where all the breaks in DNA are repaired by DNA ligase
- Double stranded break is accurately repaired
How is a heteroduplex structure formed?
- Synapsis catalysed by RAD51 and other proteins
- Binds to 3’ single stranded end of damaged DNA
- Forms a dynamic 3- stranded structure with ds-DNA
- ‘Searches’ for homology
- Structure is formed
Is homologous recombination repair of double strand breaks reciprocal or non-reciprocal?
Non-reciprical
What is lost during homologous recombination can repair double strand breaks?
Local loss of heterozygosity
DNA double stranded break repair by homologous recombination can occur in:
1) a haploid yeast cell in G1 phase of the cell cycle
2) human gametes
3) polyploid plant cells
4) somatic mammalian cells
A. 1) and 2)
B. 1) and 4)
C. 2) and 3)
D. 3) and 4)
D
What are the two main ‘jobs’ of homologous recombination?
Repairing double strand breaks and generating crossovers
How does meiotic homologous recombination generate crossovers?
- Pair of homologous chromosomes
- SPo11 and Mre11 nuclease complex break the double strand on one chromosome
- Spo11 removes a part of that chromosome and exposes single stranded 3’ end
- RecA-type strand exchange protein loaded (strand invasion
- Forms d-loop going the two chromosomes
- DNA Synthesis followed BY DNA ligation
- Forming double holiday functions
- The are two alternative paths which resolve holiday junctions by breakage and joining of DNA
- First way: cutting DNA strands in the same plane producing a chromosome without crossover
- Second way: cutting DNA strands in the different plane producing chromosomes with a crossover
What is an holiday junction?
branched nucleic and structure containing four double stranded arms joined together
What is linkage analysis?
Genes on a chromosome are linked both physically and genetically
Is it proportional or disproportional relating to recombination frequency and distance apart for two linked genes?
Proportional
Finish the sentence:
Genes further apart have…
a higher recombination frequency
What can be exploited for gene targeting?
Homologous recombination
What is gene targeting?
Targeting specific gene mutation in vivo via introducing DNA containing homologous sequences and selectable markers which are integrated in to DNA
Describe gene targeting with a circular DNA:
- Single crossover of SEL (circular DNA)
- Insertion of the gene into chromosome
Describe gene targeting with linear DNA:
-Double crossover of SEL (linear DNA)
-The gene is deleted from the chromosome and replaced with the SEL
-
Give examples of gene targeting with linear DNA:
- Yeast gene deletion
- Knockout mice
Describe homologous recombination in bacteria with circular DNA:
- Chromosome and other DNA (e.g plasmid) present
- Region og homology
- Two parts of the DNA are fused together
Describe homologous recombination in bacteria with linear DNA:
- Homologous DNA and chromosome present
- Genetic recombination replaces a section of the chromosome with homologous DNA
What can bacteriophage do within in bacterial cells?
Infect and reproduce
Can recombination occur in bacteria via bacteriophage?
Yes
Describe homologous recombination in bacteria with bacteriophage:
- Bacteriophage inserts phage DNA
- Recombination occurs in the cell (ignoring the chromosome)
- Recombinant phage produce
What is the bacteria to the bacteriophage during homologous recombination?
A host to reproduce
