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Flashcards in recombination Deck (30):
1

when does homologous recombination occur

prophase of meiosis 1- DNA already replicated

2

crossing over is visible at

chiasmata

3

if non homologous recombination occurs..

sterile

4

what is involved in homologous combination

the breaking and joining of DNA -reciprocal and causes genetic rearrangement

5

for recombination to occur..

homologous sequences must be present

6

homologous combination is an important part of..

-meiosis and variation -DNA repair

7

to repair non-homologous end joining

the double strand is broken. degradation after this causes a loss of nucleotides, but because the two lengths are now straight instead of 'sticky', the double strand can rejoined by ligase enzymes--> there will be some deletion of DNA sequence

8

homologous recombination can..

repair double strands

9

homologous recombination-simple

sister chromatid is positioned next to the double stranded break. There is a loss of nucleotides due to degradation, which removes the 'sticky' ends. When the ends have been processed, homologous recombination occurs and the damage is repaired accurately using inform from sister chromatid

10

linkage analysis

genes on a chromosome are linked (physically and genetically). For two linked genes: recombination is proportional to distant apart. Therefore if we measure RF, we can map genes

11

for two linked genes:

recombination is proportional to distant apart. Therefore if we measure RF, we can map genes

12

RF

recombination frequency

13

Gene targetting

we can target specific genes for mutations in vivo. DNA is introduced which contains: homologous sequences and selectable markers. The DNA is then integrated into the DNA causing recombination

14

In circular DNA

only single crossovers

15

in linear DNA

double crossover- and a gene will be deleted

16

detailed: how does meiotic homologous recombination generate crossovers

1) paired chromosomes are adjacent to each other 2)enzymes cause one of the double strands to break 3) exonuclease expose single stranded 3' end 4) another enzyme causes the strand to invite the other double strand on the other chromosome 5) this produces a d loop 6)DNA synthesis occurs - forming a holiday junction 7) DNA ligase cuts either across the junction or diagonally down

17

holliday junction

a cross-shaped structure tat forms during genetic recombination- when two double stranded DNA molecules (chromosomes) becomes separated into four strands in order to exchange segments of genetic information

18

depending on the way the holiday junction is cut there will either be

cross over or no crossover

19

if both chromosomes are cut horizontally

no crossover

20

if the chromosomes are cut diagonally

crossover

21

double strand break repair by homologous recombination (part 1)

  • first one of the chromatid double strand breaks
  • exonucleases degraded 5' en 
  • the overly 3' end that ahsnt been degrades, invades the sister chromatid strand
  • when they cross it is called a branch point and this heteroduplex is called a D- loop is formed 
    • then dna sytnehsis and migration of the branch point occurs

22

double strand break repair by homologous recombination

(part 2)

  • continued branch migration, followed by pairing off newky synthesised DNA with tip strand synthesis 
    • DNA; ligation - DNA Ligase attaches new DNA 

23

Heteroduplex formation in homologous recomibination 

1. synapsis is catalysed by RAD51 and other proteins

2.binds to single stranded 3' end of damaged DNA

3. forms a dynamic 3-stranded structutre with double stranded DNA

4.searches for homology

5.Heteroduplex formation

24

heteroduplex 

a double stranded moelcule of nucleic acid originated through the egentic recombination of single complememntary strands (form homologous chromsosomes) derived from different sources

25

in circular DNA there will be a 

single crossover

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in linear DNA there will be

a double crossover

27

for two linked genes combination is proportional to

distance apart- therefre we measure recombination frequency

-therefore we can map genes

28

holiday junction formed in 

the repairof a souble strand break

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heteroduplex synapsis is catalysed by 

Rad51 and othe rproteins

30