Lecture 9 Flashcards
Describe homologous recombination
- Prophase of meiosis I
- Homologous chromosome pair
- Crossing over- visable as chiasmata
- Breakage and joining of DNA, reciprocal exchange and therefore genetic rearrangement
Describe non-homologous end joining
cell recognise the breakage and the ends join but there is a loss of nucleotides due to degradation
Describe degradation
damage accurately repaired using info from sister chromatid, digest away 5’ end which have hydroxyl group ends so DNA replication can occur, homologous becomes unwound and the 3’ invades to create a D-loop and the 3’ end acts as a start point for replication, DNA polymerase synthesises new DNA from 3’ end from one strand as a template
How can homologous recombination repair double strand breaks
• Break is accurately repaired • Universal and non-reciprocal • But note local loss of heterozygosity • Can generate crossovers o Meoisis, breakage and joinage, reciprocal and genetic rearrangement
Where can double stranded break repair occur?
polyploid plant cells and somatic mammalian cells
Describe Holliday junction in meiosis
- 4 strands of DNA
- 2 homologous chromosomes recriprcally exchange DNA strands
- Stablisted by helicase proteins with use ATP hydrolysis to move the junction up and down the DNA
- Resolution – breakage and joining of double DNA strands
Describee linkage analysis
linked physically and genetically – work out how far they are apart by measuring recombination and distance
How is homologous recombination exploited for gene targeting
introduce homologous sequences and selectable marjer on a plasmid
Describe recombination in bacteria
region of homology can be inserted into DNA