Lecture 9

Question 1

Describe homologous recombination

Answer 1

• Prophase of meiosis I
• Homologous chromosome pair
• Crossing over- visable as chiasmata
• Breakage and joining of DNA, reciprocal exchange and therefore genetic rearrangement

Question 2

Describe non-homologous end joining

Answer 2

cell recognise the breakage and the ends join but there is a loss of nucleotides due to degradation

Question 3

Describe degradation

Answer 3

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

Question 4

How can homologous recombination repair double strand breaks

Answer 4

•	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

Question 5

Where can double stranded break repair occur?

Answer 5

polyploid plant cells and somatic mammalian cells

Question 6

Describe Holliday junction in meiosis

Answer 6

• 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

Question 7

Describee linkage analysis

Answer 7

linked physically and genetically – work out how far they are apart by measuring recombination and distance

Question 8

How is homologous recombination exploited for gene targeting

Answer 8

introduce homologous sequences and selectable marjer on a plasmid

Question 9

Describe recombination in bacteria

Answer 9

region of homology can be inserted into DNA